That concludes our live page coverage - you can read the news story on today's events here.
- UKIP's Mark Reckless won Rochester and Strood by-election, beating the Conservative Party by 2,920 votes
- Breakdown: UKIP - 16,867; Conservatives - 13,947; Labour - 6,713; Greens - 1,692; Lib Dems - 349
- Voters in Rochester and Strood voted on Thursday to choose a new Member of Parliament
- The vote came less than six months before the next general election
- Reckless visited Westminster on Friday morning and was sworn in as Rochester and Strood's MP
So it's been a busy day in British politics, as former Tory MP Mark Reckless wins the by-election in Rochester and Strood for UKIP.
Mr Reckless said that if his party can win there, "we can win across the country". UKIP's leader, Nigel Farage, said he believed the number of seats that UKIP could win at the general election in May had "probably doubled".
Prime Minister David Cameron said he was "absolutely determined" to win the seat back for the Conservatives next year. Ed Miliband said the result was a "devastating" setback for Mr Cameron and he was determined to meet the challenge posed by UKIP.
Away from the action at the polls, shadow attorney general Emily Thornberry resigned from the Labour front bench after being accused of "sneering" by tweeting a photo of a Rochester house with England flags and a white van outside, prior to the vote.
Meeshell Fooko tweets: Deeply dispirited by the UKIP victory in #RochesterandStrood. I always hope people will be better than they prove to be
Here's a round up of how Friday's newspapers have been covering the events in Rochester and Strood.
Writing in the Financial Times, Janan Ganesh said the Conservative party benches are "peppered with cranks, zealots and the flamboyantly disloyal".
The Guardian's political editor, Patrick Wintour, wrote that "the nature of by-elections is that they are of little intrinsic significance: their importance lies in their consequence".
In the Independent, Oliver Wright wrote that: "Rochester was not considered fertile Ukip territory. The seat is more affluent, young and ethnically diverse than the seats Ukip has traditionally targeted and Mr Reckless did not have the same personal following as Douglas Carswell."
The Daily Mail said the Conservatives "tried to put a brave face on the defeat" but overall the result was "embarrassing for David Cameron" and "humiliating" for the Liberal Democrats.
Writing in the Telegraph, senior political correspondent Christopher Hope reported that the win was "further evidence that Ukip's hold on British politics is strengthening".
And the Mirror reported that David Cameron's "hopes of regaining Downing Street in May's general election are threatened by UKIP's surge in the polls".
Glen Mitchell in Salford tweets: Cameron's determination to resting and now win back #RochesterandStrood looks slightly obsessive and vindictive towards Mark Reckless.
BBC South East political editor Louise Stewart has been looking at the potential fall-out from the Rochester and Strood by-election.
She says: "If any of the main party leaders were complacent about UKIP before, they're certainly not now."
Her blog can be found here.
One of the first senior Lib Dems to speak to the media, party president Tim Farron, quips that in his time on the doorstep in Rochester he probably met every Lib Dem voter there.
He admits the Lib Dems had a "frustrating" by-election, adding that "we couldn't get into the story" and voters had "boiled it down to two candidates".
But in comments to BBC Radio 4 he rejects the idea they should be pessimistic about the general election, saying politics is now "very fluid" and it's "highly unlikely" one party will form a government in 2015.
Tim Sculthorpe, parliamentary editor at the Press Association, tweets: Emily Thornberry is at the bar of the House chatting to Labour MPs. Looks like commiserations rather than condemnations from here.
- Copyright: BBC
It is highly unusual for a by-election winner to be sworn in to the Commons on a Friday - as Mark Reckless was, hours after winning the Rochester and Strood seat for UKIP.
A House of Commons spokesman said the last time this happened was on February 17 1956, when Edward du Cann took his seat for Taunton.
The World At One has been asking Labour MPs for their reaction to the tweet by Emily Thornberry that led to her resignation.
Ian Austin, Labour MP for Dudley North, condemns her actions as "unbelievably unhelpful" because it gave the impression that Labour is "run by an out-of-touch metropolitan elite". He also stresses that the England flag "does not belong to the far-right".
Deputy Labour leader Harriet Harman weighs in on the criticism, saying "it created a misperception of what Labour is about". She adds that the party has MPs and councillors "from all different backgrounds - we are of and for working-class areas".
- Copyright: PA
BBC Radio 4 has also heard from UKIP MP Douglas Carswell - seen here out on the campaign trail with Mark Reckless earlier this month.
He insists people voted UKIP for a range of reasons and that the party only mentioned immigration "once" on its leaflets in the Rochester by-election.
The MP for Clacton describes his party as the only one which will deliver "fundamental reform".
Dave Alcock from Kent tweets: Michael Gove called #RochesterandStrood wipeout a "very good" result on #bbcdp. Wonder what a bad result looks like?
Also on The World At One, transport secretary Patrick McLoughlin says he's "disappointed" at the result but that now the priority should be persuading people that the Conservatives "can deliver a strong economy".
Conservative MP Andrew Bridgen tells BBC Radio 4's The World At One the prime minister needs to renegotiate the terms of Britain's EU membership and, if that doesn't happen, to lead the campaign for a "No" vote in an in/out EU referendum.
He adds that he won't be the third Tory MP to defect.
Amanda Brett from Yorkshire tweets: I do wonder why more people didn't go and vote in #RochesterandStrood. Now they've got a UKIP MP! Makes no sense.
- Copyright: BBC
In case you haven't seen it yet, there's a handy compilation of numbers, maps and tables charting UKIP's polling strength in different constituencies now available here.
Glyn Edwards from Wirral tweets: Can't believe Monster Raving party got 151 votes in Rochester to Lib Dems 349! How Clegg is still leader is a joke! #RochesterandStrood
Veteran Labour MP Austin Mitchell says former shadow attorney general Emily Thornberry was "daft" to resign over a tweet and it showed that Ed Miliband was "motivated by panic".
He told the Huffington Post UK, her departure was "totally unnecessary" and the resulting furore was a "storm in a teacup".
Mr Mitchell, who plans to stand down from his Grimsby seat in 2015, said: "The leader has bigger things to worry about. He shouldn't have his acolytes running about getting people to resign over trivia."
Jonathan Sebire from Highgate tweets: I'd like to see this list of 270 seats @UKIP are touting as, now presumably 'very', likely winnable seats. #RochesterandStrood
- Copyright: BBC
Speaking to the BBC while on a visit to a school, Ed Miliband says there are "wider lessons" to learn from this by-election.
"We know we've got a challenge in relation to UKIP. It's a challenge I'm determined to meet," he vows.
Asked how he would meet that challenge, Mr Miliband replies: "I think what it says is there is deep discontent about the country and there is also scepticism about whether any mainstream party can turn it around.
"Our fight, our job, is to show we can."
The BBC's Westminster team reports that the man whose house was photographed by Emily Thornberry in that controversial tweet is thought to be heading to the Labour MP's Islington constituency with a large flag.
Ed Miliband has also been speaking about the tweet sent by Labour's Emily Thornberry. He says it "conveyed a sense of disrespect" and "that's why I was so angry about it".
Mr Miliband says her intention "may not have been" to be disrespectful but adds: "I was angry because I thought her tweet gave a misleading impression, when she photographed the house in which the family lived, that somehow Labour had the wrong view of that family.
"It's not the view we have of that family. Labour's never had that view, of disrespect."
Labour leader Ed Miliband tells the BBC: "I think the most important thing about these results is that it was a devastating result for David Cameron."
He adds that in his view the Conservatives "lost and lost badly".
Also in that interview with Nick Robinson, Nigel Farage gave some more details about the policies his party would pursue.
He said he "obviously" favoured tax cuts, "particularly for the low paid, the idea that anyone earning minimum wage is paying income tax is crazy".
He denied he had ever spoken in favour of more privatisation of the NHS, adding he wanted to see fewer private companies involved in the NHS as it "hasn't worked - all it's done is transfer money out of public sector to make rich people richer".
Former Conservative - now UKIP - MP Douglas Carswell says the Conservative Party has plenty to ponder following the by-election result.
He said: "If the Conservative Party think that all is well then they've got an even bigger problem than the rest of the country thinks they've got.
"Britain today is a country where pretty much everything is run in the interests of vested interests. Politics, banking, the energy markets - they're all run by this self-serving little clique at the top."
Nigel Farage has told BBC Political Editor Nick Robinson he believes the number of seats UKIP can win in next year's general election has "probably doubled" following the by-election result in Rochester and Strood.
He refused to be drawn on whether UKIP would support David Cameron or Ed Miliband in any possible coalition agreement, saying UKIP would do a "deal with the devil" if it meant they could get what they want.
When asked if his party supported spending cuts or spending increases, the UKIP leader said: "Spending cuts and here's why; I think one of the real elephants room of British politics is that by at end of lifetime this parliament of national debt will have increased by 40%."
Ed Miliband's newly appointed campaign deputy, Lucy Powell, tells the Daily Politics that her colleague Emily Thornberry's tweet was "an insult" and although there were "question marks over what she wanted to say" her behaviour had been "unacceptable".
She rejected claims Labour was alienating its traditional base of working-class voters.
Al Scott from Brighton tweets: #Rochester Unintended mistake no doubt, but UKIP gain from common belief that Labour elite despise the very people they claim to represent.
Here's the moment veteran Labour MP Dennis Skinner gave UKIP's new MP a hard time mere moments after he was sworn into the Commons. He passionately accused Mark Reckless and his UKIP colleague Douglas Carswell of wanting to deport foreigners.
- Copyright: BBC
Continuing his interview on the Daily Politics, Mr Gove says voters were sending a message to the government that it needs to "sharpen up" and that the Conservatives have heard the message.
Asked if he did enough as chief whip to prevent Mr Reckless' defection, Mr Gove replies: "If people choose to say one thing and do another they say there's very little I - or anyone else - can do."
Eddie Eldridge from Gloucestershire tweets: One reality from #RochesterandStrood is that Tory pledges on Europe were simply not believed. Cameron needs to get that referendum rolling
Michael Gove, the government chief whip, tells the Daily Politics it was "a very good result - governments don't tend to win by-elections". He says "most dramatic thing has been the haemorrhaging of the main opposition party".
Following the Rochester and Strood by-election results, John Baron, MP for Basildon and Billericay, says the Tories are the only party to be trusted to hold an EU referendum.
"The fact remains that only the Conservatives are willing and able to deliver a much-needed in/out referendum after the next general election. The Labour and Liberal leaderships won't, and UKIP can't.
"Despite their many broken promises about referenda, Labour and the Liberals should be ashamed they arrogantly do not trust the electorate to make the right decision on this very important issue. A referendum is essential."
- Copyright: BBC
Patrick O'Flynn, UKIP MEP, is on the Daily Politics this lunchtime. He dismisses the idea that a vote for UKIP is a protest vote and people will revert to larger parties at the general election as "a comforting narrative".
Pressed on whether there will be further defections, Mr O'Flynn says: "I really don't know. I know there are MPs seriously considering their positions."
On the furore over Emily Thornberry's tweet, Seb Payne from the Spectator says Labour leader Ed Miliband's reaction seemed "panicked" because he was rushing "to do something not to seem weak", and it was not the right decision for her to leave her front bench post.
SNP MP Pete Wishart tweets: My advice to the W'ster establishment parties is don't attack UKIP in the House like they do the SNP. It'll help them like it has helped us.
Seb Payne, online editor of the Spectator, tells BBC Radio 5 live the Conservatives "were always going to put that spin on it - that they haven't done as badly as expected", but points out conversely UKIP did not do as well as expected.
He predicts Mr Reckless "is going to struggle" in the 2015 as he doesn't have as great a margin of victory or as close a personal following as the other UKIP MP, Douglas Carswell.
Tory MP Mark Field tells the BBC that the situation was "disappointing" for the Conservatives.
He added: "In many ways, the appeal [of UKIP] isn't Europe or immigration alone, it's a cultural two fingers up to the entire political process. That's something all politicians have to be aware of."
Alex Christopher tweets: The #RochesterandStrood by-election result should be of no surprise, yet somehow Tories and Labour have ended up soul-searching for answers.
Dan Ware, 37, is the man whose van and house in Rochester was tweeted in a picture by Labour's Emily Thornberry.
He told the Sun: "To me it just proves Labour is full of the upper classes. I would never vote Labour now.
"I think they need to get out of their mansions and visit the working class. Her and Ed should come and say sorry to me."
Mark Reckless concludes his first speech in the Commons as an elected UKIP MP by telling MPs he is "very sceptical" of the US-EU trade deal TTIP, which has the prime minister's backing. You can read more about TTIP here.
BBC News political editor Nick Robinson tweets: Why @Ed_Miliband condemned white van/England flag tweet : "conveyed a sense of disrespect. Not my view, not Labour's view, never will be"
Assistant political editor, BBC News
I don't smell fear in the Tory party. Last night it was very noticeable the Tory MPs and staff were sitting around, chatting with us. They were pretty relaxed, they weren't quaking in their boots.
I also look at the reaction in Westminster. There has not been a sort of clamour for Cameron to get his act together and I think within Tory ranks they think they can win this seat back at the next general election. More than that, I think they are beginning to wonder as to whether the UKIP bandwagon might just be slowing down.
Albeit, listening to Mr Farage this morning, he was adamant that the next general election is entirely up for grabs.
Mr Reckless is taking part in the National Health Service Bill debate, which can be followed live here.
Mark Reckless is making his Commons debut as a UKIP MP, hours after being sworn in.
Thomas Devlin in UK tweets: One reality from #RochesterandStrood is that Tory pledges on Europe were simply not believed. Credibility deficit not reducing!
- Copyright: BBC
Mark Pritchard, Conservative MP for the Wrekin, Shropshire, tells the BBC he won't be defecting to UKIP, saying: "My beating heart is Conservative."
He admits he is an "arch Eurosceptic" but adds: "UKIP are all things to all people. They're sort of the modern equivalent of the Liberal Democrats."
Mr Pritchard also praised the Green party for increasing their share of the vote.
Andy Clift tweets: Honestly #RochesterandStrood, how is voting in the same dude a vote against the status quo?
BBC Radio Kent has been taking calls from listeners about their views on the result.
"I feel there's been a lot of negative campaigning, particularly from the Tories. I think the political system is broken and I think that's why so many people are voting UKIP," says Malcolm Hazleton, from Strood.
Pam McHale, from Rochester, says she voted for Labour after thinking "long and hard". She adds: "In the end I couldn't possibly vote for the Conservative whose values and views were nowhere near my own."
Roger Steare in London tweets: UKIP victory at #rochesterandstrood will shake up our arrogant and cosy political elite. Time for a debate about political philosophy
Paul tweets: #RochesterandStrood The result shows further disillusion with the current political climate and further misunderstanding of UKIP's policies.
Talking to BBC Radio Kent, Hayley Mills, from Rochester, said: "I don't know whether [Reckless] will be a permanent fixture, I think most people probably have voted UKIP because they've tapped into a discord that people are identifying with.
"I'm not sure if it's just personal ambition from Mark, or whether he really understands the constituency he's representing."
Labour's Emily Thornberry has issued a statement following her resignation as shadow attorney general, after sending a tweet which was widely deemed offensive.
"What I want to say is I got it wrong, I made a mistake, I've resigned and if I've upset anyone or insulted anyone, I apologise, I'm going in this morning for a really important bill for my constituents which is about the privatisation of the National Health Service which we've got to stop, so I'm going in now because I'm serving my constituents."
Graham McDougall tweets: #RochesterandStrood The people want a competent government who have integrity. What choice are we given? The status quo is not good enough.
Mark Reckless has urged more MPs to join UKIP. In an exclusive BBC interview, Mr Reckless said he would not predict how many more Conservatives might defect to UKIP because it was a "very individual decision". But he pointed to the party's record.
"We may be two MPs but we represent millions of voters," he said. "If you look at the impact Douglas (Carswell) has had just as one MP in terms of what the prime minister has been saying, what the opposition are now saying on issues that UKIP have campaigned on."
political correspondent, BBC News
UKIP's new MP, Mark Reckless, has already come under fire in the Commons - just moments after being sworn in.
The veteran Labour MP, Dennis Skinner, pointed at Mr Reckless and his UKIP colleague Douglas Carswell and accused them of wanting to send foreigners back to their country of origin.
Earlier this week, Mr Reckless was accused of suggesting that some Europeans living in the UK might have to leave if the UK left the European Union - something he later said was not the party's policy.
Will Holmes tweets: Every vote for UKIP is a small but significant step backwards for humankind #RochesterandStrood
Speaking about the tweet sent by the shadow attorney general - for which she later resigned from Labour's front bench - Mr Cameron said: "Emily Thornberry is one of Ed Miliband's closest allies and aides.
"Effectively what this means is that Ed Miliband's Labour Party sneers at people who work hard, who are patriotic and who love their country, and I think that is absolutely appalling."
- Copyright: PA
The prime minister has just been seen at Paddington station in central London, after his party lost the seat of Rochester and Strood.
Prime Minister David Cameron says of the Rochester and Strood result: "I am absolutely determined to win this seat back at the next general election because anything other than a Conservative government will put our recovery at risk and Ed Miliband in Downing Street. I am more determined than ever to deliver security for Britain."
Dave Poole tweets: Reckless has already been sworn in as #UKIP MP for #RochesterandStrood. This House of Commons is starting to take shape nicely!
- Copyright: BBC
The BBC's Robin Brant tweets this picture with the message: "Here's @Ladbrokes take on a 3rd defector."
Claire Mansfield in London tweets: Surely all #rochesterbyelection proves is don't underestimate the power of the personal vote.
There was some heckling from Labour MPs as Mark Reckless took the oath - but the Conservative benches were largely empty.
It is unusual to be sworn in on a Friday. The Commons ordinarily only takes backbench bills and often does not sit at all.
Steve Bedder emails: "I agree with Bry and the swing to UKIP is a protest vote which is not seen as a wasted vote. Looking ahead, if there was a box on the General Election ballot paper marked "none of the above" then would there be a swing from UKIP to this protest vote?"
- Copyright: Douglas Carswell
Mark Reckless's fellow UKIP MP Douglas Carswell tweeted a photo of the pair, with the message: "Selfie selfie! Woohoo!".
Mark Reckless said after being voted back as MP for Rochester and Strood - albeit for a different party - how he "thought [going] straight back to work was the best thing".
Prime Minister David Cameron says he is "absolutely determined to win" the Rochester and Strood seat back for the Conservative party, following Mark Reckless's victory there for UKIP.
- Copyright: BBC
Mark Reckless is seen here being sworn back in as a Member of Parliament at Westminster, this time as a representative of UKIP.
Sarah Louise Stewart in Kent tweets: Oh no. Very disappointed but not overly shocked at the UKIP result in Rochester. Staying hopeful its just temporary #rochesterbyelection
Mark Reckless has been sworn in at Parliament. Douglas Carswell, the first Conservative defector to be elected for UKIP, and Conservative MP Philip Hollobone escorted Mr Reckless into the chamber at the Houses of Parliament.
Steve Buc emails: "The common argument against UKIP is that they don't have any policies. They do however, have principles and will deliver those. The other parties do have those treasured policies, but don't deliver on them in any case. So the argument about policies is weak."
BBC Radio 5 live wants your views, and has tweeted details of how to get in touch: "Your Call: UKIP has won its second by-election. Is #UKIP for you? Call 0500 909 693."
Matthew Harrison in Manchester tweets: #UKIP have won two seats without the MP changing. Odd to claim victory over anyone other than the #Tories. #RochesterandStrood
- Copyright: Mark Reckless
Mark Reckless has tweeted this picture of himself outside the Houses of Parliament, with the message: "With my Certificate of Return to swear in at 9.30am. Thanks to @vincemaple and Medway Labour for arranging."
You can watch a report on UKIP's win in Rochester by the BBC's political correspondent, Chris Mason, here.
Graeme emails: The main political parties still don't get it -we are sick of "career" politicians telling us what's best for us and of Europe's total lack of democracy-watch this space people like upsetting "them" and that is what is going to happen!
Those fancying a flutter may be interested to learn William Hill has placed UKIP as 4/11 favourites to retain the Rochester and Strood seat at next year's general election. The Conservative party are at 2/1 to win it back. Further out are Labour at 20/1 and you can get 200/1 for the Lib Dems.
Thanet North Conservative MP Sir Roger Gale tells BBC Radio Kent: "I think Kelly Tolhurst will be the MP for Rochester and Strood in May 2015."
Andrew John in West Wales emails: While I would not vote UKIP - because they're Tories by another name - it's good to see the real Tories getting a pasting.
BBC political correspondent Vicki Young tweets: After his victory Mark Reckless tells me he celebrated with an orange juice, several cups of coffee and then did emails.
Green candidate Clive Gregory believes his party was a victim of tactical voting in Rochester.
He says: "I think had we got everyone who wants to vote Green to vote Green we'd definitely been in with a deposit-saving situation and maybe even pushing into the high [vote share figures], even towards 10%.
"We feel that's actually regainable for the general election and as soon as this finishes we're back on the campaign working towards that."
Mr Gregory said the Green Party was the only "true opposition" and five seats at the general election was a realistic possibility.
Aiden tweets: The tables are turning, the people have spoken. Well done #RochesterandStrood for electing #MarkReckless positive change is happening. #UKIP
- Copyright: EPA
The Tory candidate in Rochester and Strood, Kelly Tolhurst, tweets: "Massive thanks to all who've voted for me. To my campaign team & my family - I couldn't have done #RSvote without you - you've been amazing."
Bry emails: I believe that both major parties have become so unpopular that the general public is voting for an alternative, rather than voting for issues such as immigration.
Mr Farage said UKIP won in Rochester because it did not just get Conservative votes. "We got Labour votes... we got Lib Dems. The Conservative make-up of our vote last night was a minority of the votes that we picked up."
Mary-Ann Jones in West Midlands tweets: .@ukip Can you enlighten me on your housing & planning policy? One issue party perhaps? Better get the pens out #UKIP #RochesterandStrood
- Copyright: BBC
Here's Rochester and Strood's newest MP, who looks remarkably like the previous one. Vicki Young, BBC political correspondent, tweeted this picture, writing: "Mark Reckless arrives in London after no sleep following by-election victory #UKIP."
Rochester resident Angela Rahman, editor of Nubia Magazine, who was born in Manchester to Jamaican parents, told BBC Radio Kent she was very concerned about the by-election result because UKIP "represents everything to do with anti-immigration, so that's scary for me".
- Copyright: BBC
Nigel Farage, talking to BBC Breakfast, says that "from Birmingham, up to Hadrian's Wall, if you vote Conservative, you will get Labour, because UKIP is the only challenger there".
He added: "We want this country to have a referendum to decide whether we govern our own country or not. That referendum will only happen if we only get enough UKIP MPs into Westminster on May 7th next year. What happened last night in Rochester takes us a massive step forward on that route."
The Guardian's political editor, Patrick Wintour, writes that "the nature of by-elections is that they are of little intrinsic significance: their importance lies in their consequence".
He adds: "Overall, the Rochester result does not seem such a thunderbolt, or so unexpected that the Tory party will self-destruct. If so, that places some pressure on UKIP to retain momentum".
Conservative Leader of the House of Commons, William Hague, tells BBC Radio 4's Today programme: "We will work every day from now to the general election to make sure we get this seat back at the general election. I think there is every prospect of doing so."
Gabriel Stirling in Aldermaston Wharf tweets: Labour needs to return left wing policies if it's to regain support after #rochesterbyelection
Mr Farage dismisses the idea that Labour could mount a fight-back against his party.
"I doubt they can make those inroads under this leader," he says. "Labour have increasingly become anti-English, happy to pander in every way to Scotland. New Labour believes any sense of English identity is disreputable and wrong."
James Birdseye in London tweets: The major story of #rochesterbyelection is the total collapse of @LibDems. National outlook, virtual end of party in 2015.
Some more from Nigel Farage from the Today programme. The UKIP leader defended the debate within his party on whether the NHS should be privatised.
He says: "The idea we get from Andy Burnham and the Labour Party that it's immoral and wicked to have a debate about how we might do things differently is what led to Mid Staffordshire and so many disasters."
BBC political correspondent Vicki Young tweets: Waiting at not very secret location for arrival of @MarkReckless he didn't get this kind of attention as a Tory backbencher
Janan Ganesh, writing in the Financial Times, says the Conservative party benches are "peppered with cranks, zealots and the flamboyantly disloyal".
As for Labour, he says the cultural gap between its "working class voters and its London-based doyens is not new. But it has become unbridgeable under Ed Miliband's leadership".
Naushabah Khan, Labour's by-election candidate, says she is "disappointed" by the result but proud of the "very positive" campaign that was run.
She adds: "I was selected here a year ago to fight an election in May 2015 and that's what I intend to do. I'm going to be out next year and I'm going to take from this election the things that I've learnt, the stories that I've heard from people, and they're the issues I'm going to continue to fight for."
Adam Watson in Leeds tweets: If we'd had a by-election in a major city, Scotland or a university seat, #UKIP would've done nothing. Remember that! #RochesterandStrood
- Copyright: AP
Here's UKIP leader Nigel Farage with his party's newest MP, Mark Reckless, taken while the counting of votes was still under way. The declaration eventually came at 04:15 GMT.
The Daily Telegraph's Tim Stanley has some advice for political parties going into future battles. "To beat UKIP and retake command of the national political narrative, the mainstream parties have to reconnect with the people and to demonstrate that they share their concerns, are being honest about the problems ahead, and have faith in the common sense of ordinary people."
Sarah Wollaston, MP for Totnes, Brixham and the South Hams
tweets: Tories have lessons to learn from the #RochesterandStrood campaign, but that must not include a lurch to right or a vile scapegoating agenda
Mr Farage adds: "Personally, I would love people to join us and force by-elections. I would love these by-elections to go on forever. The last three months have been enormous fun."
Labour MP John Mann says Emily Thornberry's tweet, showing a picture of a house in Rochester with England flags and a white van outside, was offensive.
"It was horrendous, it insults people like me. It insults the people I know, my friends and family, Labour voters across the country. Because white vans, England flags, they're Labour values and actually pretty routine Labour values for most of us."
"Who can say how UKIP will do in the general election?" asks Nigel Farage. But he adds there will be "Members of Parliament who work out that actually, they've got a better chance of standing as UKIP. If they join us, I'll be delighted. If they don't, frankly it doesn't matter".
Emma Appletonno in Wigan tweets: surprise we won #rochesterbyelection. Being asked to throw their hard earned money at EU sinking ship prob turned a lot of torys UKIP!
Nigel Farage, speaking to BBC Radio 4's Today programme, says he would "ignore every one of the political commentators" and predicts "there will be a lot of sucking of teeth" over the coming weeks.
The BBC's political editor Nick Robinson says in a blog post that UKIP has "certainly shown it can defeat everything the Conservative party machine can throw at it - money, manpower, five campaign visits by a prime minister and, yes, even that kitchen sink David Cameron promised to throw in too".
UKIP leader Nigel Farage tells the BBC that the result of the next general election has been "thrown up in the air".
"Things are changing out there very, very quickly," he says.
The Conservative party's William Hague says UKIP's margin of victory was less than half what the party and polls were predicting.
"We will work every single day between now and the general election to make sure we win this seat back at the general election, because we're not going to let UKIP let Ed Miliband sneak into Downing Street by the back door. And that is clearly the danger here".
BBC Radio 5 live spoke to voters in Rochester while polling was open, with one resident describing UKIP leader Nigel Farage as a "saint". You can hear their views here.
Oliver Cooper in London tweets: No major party has ever won less than 1% of the vote in a parliamentary by-election. Until the Lib Dems in #RochesterAndStrood.
YouGov president Peter Kellner tells BBC Radio 4's Today programme it is too early to say what will happen at the general election next May.
He says: "I don't think that Mark Reckless's cushion is big enough either for him here in Rochester next May, or for other Conservative MPs who are thinking of defecting."
Leader of the House of Commons William Hague tells BBC Breakfast that people are concerned about immigration and the European Union and commonly express their anger in by-elections.
"It's very unusual, actually, for the Conservatives in government to win a by-election," he says. "That's only happened once in the last 25 years, even though we've won many general elections."
Tom Mludzinski, head of political polling at ComRes, tells BBC Radio 5 live Breakfast's Nicky Campbell: "It certainly does show that UKIP are on a march. It carries on the momentum they have been building.
"Many people, including myself, have predicted that at some point they will have peaked over the last few years, perhaps at local elections or European elections, and yet they keep on going. They are taking the fight to all sides."
Jack Roach in Kent tweets: So @UKIP have won the #RochesterandStrood by-election. Now, I wonder if Reckless will actually do something to help his constituents.
Martin G Haigh in Bristol tweets: Shouldn't there be an inquiry into why LibDem candidate was not on #RochesterandStrood #byelection ballot papers? Eh? 349 votes? Ohhh...
- Copyright: BBC
The BBC's Robin Brant tweets this picture of UKIP leader Nigel Farage, with the message: "He's croaky and admits he's a little rough this morning after the late count."
Labour's Douglas Alexander tells the BBC that the shadow attorney general was right to step down over her tweet of a picture of a house draped in England flags.
"I completely understand why friends and colleagues in England are intensely proud of the flag of St George. Emily Thornberry did the wrong thing in sending that tweet. She did the right thing in resigning."
UKIP also has its first elected member on Medway Council. Councillor Chris Irvine, who defected from the Conservative Party in September, received 2,850 votes, pushing the Tories into second place in the Peninsula Ward by-election.
He told BBC Radio Kent he switched to UKIP over the Conservative-led council's plans to build thousands of new homes at Lodge Hill.
BBC Radio 5 live tweets the question of whether the by-election result is a game changer - with John Pienaar saying: "The laws of political physics are being rewritten."
Douglas Alexander adds: "Of course, in truth, there are lessons for all of the main political parties given not just the result we saw last night, but the results we've seen in other recent by-elections and in the European elections earlier this year."
The Independent's Oliver Wright says the first-past-the-post election system means UKIP "are very unlikely to win more than four or five seats next May. In fact, its small majority in Rochester suggests that Mr Reckless may well be booted out from his seat in just a few months time".
But, he adds, if the party can succeed in taking 10-15% of the vote in the 100 or so marginal seats that will determine the next election, "then they could have a disproportionate impact on the overall result".
Alaister Jeffrey in Scotland tweets: No major party has ever won less than 1% of the vote in a parliamentary by-election. Until the Lib Dems in #RochesterAndStrood.
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Labour's shadow foreign secretary Douglas Alexander tells BBC Breakfast: "David Cameron threw the kitchen sink at this seat but he lost. It's something of a humiliation for the prime minister."
Historian Tim Stanley writes in the Telegraph: "Out of this slide towards metropolitanism, only UKIP has managed to project a sense of 'getting' hard pressed voters. People don't necessarily agree with Farage or even possibly like him. But they know what he is; they understand a man like that."
BBC political correspondent Robin Brant tweets: @UKIP donor tells me they are targeting 40 'winnable' seats now. More details on @BBCBreakfast
Priti Patel, Conservative MP for Witham in Essex, tells the BBC's John Pienaar it is a "disappointing result" but says it was "a tight margin." She adds: "We fought a good campaign and we're proud of that."
Conservative peer Lord Ashcroft tweets: The Conservative Party shouldn't get too cocky about winning Rochester back at the GE. A positive rather than a negative campaign needed.
Haniya Khalid in Glasgow tweets: Interesting night eh, though by no means surprising-u know, except that #WhiteVanGate bombshell. #RochesterandStrood #Rochester #UKIP
Some more thoughts on the Lib Dem turnout - Christopher Hope, senior political correspondent at the Daily Telegraph, tells BBC Radio 5 live's chief political correspondent John Pienaar: "It's dreadful for them. We're seeing a cratering across the country of Lib Dem support."
Cameron Penny, in London tweets: #RochesterandStrood Ukip margin not enough to win at #GE2015, @UKLabour damaged, @LibDems destroyed, good night for @TheGreenParty
Marcher Lord tweets: I think there's something wrong with my laptop. It says the LibDems only got 349 votes in #RochesterandStrood
- Copyright: EPA
The leader of the Official Monster Raving Loony Party, Howling Laud Hope, seen here on the right with his party's candidate, Hairy Knorm Davidson, added a bit of colour to the election results evening. Their party pulled in 151 votes.
On the low Lib Dem vote, Professor Andrew Russell, head of politics of Manchester University, tells BBC Radio 5 live: "I think it's the lowest performance by any of the three main parties for at least two or three generations. And it's almost certainly the lowest performance in a by-election for any party of government."
Assistant political editor
For the Tories, the result was not perhaps the meltdown they had feared and certainly there is no indication so far of panic, or calls for Mr Cameron to go. Senior Tories also believe they are poised to win back this seat at the general election.
For Labour, not only was their share of the vote almost halved, but there was also despair at the damaging tweet by their former shadow attorney general Emily Thornberry, seemingly mocking white van man.
As for the Lib Dems, not only were they again overhauled by the Greens but they secured a derisory 349 votes - their lowest total ever.
Assistant political editor
UKIP's victory was in many ways even more impressive than their triumph in Clacton. The ease with which they demolished a 9,000 Tory majority was striking and this after the Conservatives had strained every sinew to halt the UKIP bandwagon. UKIP now insist that no Tory seat is safe and have suggested other Conservative MPs are more likely to defect.
BBC political correspondent Robin Brant tweets: In short @ukip march conts with comfy win in non target seat, Tories humiliated despite huge effort.
Tony Cowin in Southport tweets: Lib Dems only win around 5% of the votes compared to The Green Party. Guess which one is invited to join the GE debates? #RochesterandStrood
It was a good night for the Green Party too - it outpolled the Lib Dems by almost five to one, moving into fourth place and almost trebling its share of the vote.
Tim B tweets: As a Labour supporter, I would've considered voting tactically for UKIP in #RochesterandStrood
- Copyright: Reuters
Following the country's latest by-election, here's a pictorial look back at by-election battles since 2010.
Former Tory Mr Reckless says he "would encourage people in the Conservative Party and in the Labour Party to come over and join us in UKIP."
Mark Reckless says he has a "good majority" and adds: "It's a good basis to go into May. I'll be doing everything I can in the constituency and beyond."
Stephen Lees tweets: As a lifelong Tory I have to admit that, despite the less than inspiring delivery, that was a good speech. #RochesterandStrood #bbctw
Rob Watson, UK political correspondent, BBC World Affairs Unit: "It's less of a splash perhaps than winning their first elected MP, but it's still a big deal. What's not clear is whether this is a protest vote that will disappear at the general election next May, as the main parties hope, or whether something more profound is happening in British politics.
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UKIP leader Nigel Farage leads his party's celebrations.
John Middleton in Wolverhampton tweets: Mark reckless wins the #RochesterandStrood by-election, and what a great speech by Mr Reckless at the end to round off a great day.#UKIP
Mr Shapps adds: "During the course of this campaign the gap's closed. I think we've ended up with about a 7% lead for Mark Reckless. They were predicting something over twice that level so 2,900 is not a big majority now to try to win back in 170 days time."
Conservative Party chairman Grant Shapps tells the BBC he is disappointed with the result but there are different circumstances in a by-election. He says it is not a big majority to try to win back.
Ian Ferguson tweets: #RochesterandStrood by-election....wow. Tories are in some serious trouble in May if this is any indication
This is what Mark Reckless said in his victory speech: "Thank you to the thousands from UKIP who gave up your time to campaign for me. I wish I had the words to express how grateful I am. This is your victory. As you savour it, think of this, Rochester and Strood was our 271st most winnable seat. If we can win here we can win across the country. If you vote UKIP you get UKIP."
Mark Reckless tells the BBC's This Week: "I'm pleased the people of Rochester and Strood have spoken."
Full result: Mark Reckless (UKIP) 16,867 (42.10%), Kelly Tolhurst (C) 13,947 (34.81%, -14.39%), Naushabah Khan (Lab) 6,713 (16.76%, -11.70%), Clive Gregory (Green) 1,692 (4.22%, +2.69%), Geoff Juby (LD) 349 (0.87%, -15.39%), Hairy Knorm Davidson (Loony) 151 (0.38%), Stephen Goldsbrough (Ind) 69 (0.17%), Nick Long (PBP) 69 (0.17%), Jayda Fransen (Britain 1st) 56 (0.14%), Mike Barker (Ind) 54 (0.13%), Charlotte Rose (Ind) 43 (0.11%), Dave Osborn (Pat Soc) 33 (0.08%), Christopher Challis (Ind) 22 (0.05%)
Mark Reckless: "We must be a party that speaks to and for the whole nation and all those who live in it."
Mark Reckless: "The radical tradition has found a new home in UKIP. It's UKIP that represents the concerns of most working men and women."
UKIP's Mark Reckless wins Rochester and Strood by-election.
Medway Council tweets: We are expecting the result of the Rochester and Strood By-election soon
Will immigration decide the Rochester and Strood result? Chris Mason asks local voters.
Here's that council by-election result in full: UKIP 2,850, Con 1,965, Lab 716, Green 314, Lib Dem 60.
May 2011: Three seats - Con 2,307, 2,257, 2,125, Lab 975, 898, 879, English Democrats 535, 476, Green 351, Lib Dem 298, 282.
earlier said the tweet had "given the Tory press an alternative narrative" to UKIP's expected victory in the by-election: "It is the most extraordinary self-inflicted wound I have seen an opposition party inflict on themselves in many, many years."
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Here's the picture the now former shadow attorney general Emily Thornberry tweeted during the by-election campaign.
Emily Ashton, from the Sun, tells Andrew Neil she has been talking to the man whose house, flags and van were photographed and tweeted by Labour's Emily Thornberry - who then resigned from the party's front bench after being accused of "sneering".
"He was just a bit cross to be put in the middle of a story that he didn't want to be in," she says.
The flags were from the World Cup in the summer, and he uses the van for work, she adds.
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Chris Irvine, who worked in Mr Reckless's constituency office, told the BBC: "I grew quite unhappy with the way the Conservative Party was going."
Martin Heneghan in Sheffield tweets: I give up. Too tired and we've known the #RochesterandStrood result all night. The next election night drama is #GE2015 night all #bbctw
Christopher Irvine, who followed Mark Reckless in switching from the Conservatives to UKIP, wins in the Peninsula Ward on the council.
UKIP win a by-election on Medway Council.
- Copyright: BBC
Here's Kelly Tolhurst at the count.
Mr Farage is closely followed by Conservative candidate Kelly Tolhurst, who refuses to comment on questions that she has been defeated.
Nick Millward tweets: It's a by-election Nigel - get over it. Whether you can hang onto it next May is another matter. #RochesterandStrood
Farage on Reckless: "He's shown some real guts, done the sort of thing that in politics people don't do anymore - shown principle, honour, put his neck on the line, trusted the people of the constituency and I hope that's going to be rewarded."
- Copyright: BBC
Nigel Farage arrives at the count: "I'm hoping we're going to win. I'm just here as a supporting cast for Mark Reckless."
Our correspondent Chris Mason informs us that the Official Monster Raving Loony Party have been handing out bananas while they wait.
UKIP have won one and finished second in eight of the 21 by-elections held since the 2010 general election. What is at stake for the parties?
- Copyright: BBC
Here's the scene at the count which is taking place not in Rochester but at a Medway Council sports centre in nearby Gillingham. The BBC's Chris Mason, who is there, says the result still may not be announced for a couple of hours yet.
- Copyright: BBC
Mark Reckless has arrived at the count in the glare of the photographers' flashes, saying: "I'm looking forward to the counting and hearing the result. The people of Rochester and Strood will have their say."
Chris Latimer tweets: To be honest mark reckless winning by 3 thousand has the same impact as if he would have won by 12 thousand a win is a win #bbctw
Turnout was 50.67% (40,113 votes), acting returning officer Neil Davies said.
"No-one in the Tory side is predicting that they are going to win, everyone on the UKIP side are predicting that they will."
Votes are being counted in the Rochester and Strood by-election where the UK Independence Party is hoping to gain its second elected Westminster MP. The contest was triggered by MP Mark Reckless's defection from the Conservatives to UKIP. Polls suggest he is on course to win the seat for the party.