UKIP: How far could they go?
It's a breakthrough all right but a breakthrough to what?
First and foremost to the end of the stranglehold on British politics which the two big UK parties have had for so long. British politics is now a national contest between at least four parties - Conservatives, Labour, Liberal Democrats and UKIP - and arguably five or more if you add the Greens (who are polling as well as the Lib Dems), the SNP (who are threatening Labour's many former Labour strongholds) not to mention Plaid Cymru and Respect.
Not since the emergence of the SDP in the early 1980s - after Roy Jenkins, Shirley Williams, David Owen, Bill Rodgers and others broke away from the Labour Party - has politics looked so fluid and unpredictable.
What we are seeing now, though, differs fundamentally from what we saw then. UKIP's rise is not - not yet at least - about a public desire to create an alternative party of government.
Their rise has been driven more by an anger with "all of the above", with the "Westminster parties" or what UKIP supporters like to call "the LibLabCon". In that sense - even if in no other - there are parallels between the rise of Nigel Farage and Alex Salmond.
On the morning after his victory and near-victory before, Nigel Farage talked of holding the balance of power after the next election, of becoming the Minister for Europe having won more Tory seats in the South and Labour seats in the North. How realistic is that?
Before giving the reasons why I think Mr Farage might be over-doing things just a tad it's worth pausing to say that so far his brave talk and giddy optimism has proved much more right than any of his critics or, indeed, the pundits.
They said UKIP were extremists who only a few would vote for…
They said UKIP could only win elections held under Proportional Representation…
They said UKIP would never top 30% in a poll…
They said Farage's party could only appeal to angry, former Tory blazer wearing Colonels in the south…
They were wrong.
UKIP have now proved that they can assemble a huge coalition of protest votes from the right, the left and the centre combining people who are angry about the state of the economy and the state of politics not just immigration and Europe.
The academics Robert Ford and Matthew Goodwin have studied the long term drivers of support to UKIP in their book "Revolt on the Right". They identified three - anger with Europe, anger about immigration and with the political system as a whole. A fifth of all voters shared all three concerns. Around a third shared two of the three. Thus, they conclude, UKIP's base support could be between 20% and the low 30s.
Remember that UKIP's first place in the European elections in May was the first time any party other than the Conservatives or Labour had won a national election in 100 years and, contrary to the suggestions that they are a party of the English South, they won a seat in every region as well as in Wales and, yes, Scotland too.
If they can now win the next by-election in Rochester & Strood - caused by the defection of a second Tory MP Mark Reckless - it is easy to see a few more Tory MPs following suit in an effort to save their skins before the voters get their say next May. UKIP will tell them that they have no need to risk a by-election so close to a general election.
That is Nigel Farage's dream scenario - a couple of by-election victories, a few more defections and an awful lot of momentum.
So, why might it not turn out that way?
The Tories gave up on Clacton, believing it to be unwinnable. But they are throwing the kitchen sink at winning Rochester - spending tens of thousands of pounds paying for an open primary in which every voter in the constituency is invited to help choose their by-election candidate. Douglas Carswell was an assiduous and popular local MP regarded as a man of principle who risked all to jump ship.
Tory HQ is portraying Rochester's former Tory MP Mark Reckless as a lying opportunist who has eaten his words and ditched his principles to ensure he can, in David Cameron's words, keep "his fat arse on the green benches" of the Commons. If the Conservatives win there it will stall the UKIP bandwagon and may persuade other Tory MPs not to take the risk.
David Cameron is also counting on convincing voters that the real choice to come at the general election is him in Number 10 committed to holding an EU referendum or Ed Miliband instead, who is not committed to holding one. Senior Tories are confident that this "David v Ed" squeeze will work. After all, UKIP got 16.5% in the 2009 European elections but ended up with only 3% of the vote at the 2010 general election just as the Greens got 14.5% in 1989 but did not elect an MP until 2010.
UKIP have always protested that they are as much as a threat to Labour as to the Tories. After last night's close shave in the Heywood and Middleton by-election many Labour MPs may agree with Frank Field's assessment that there are now no safe seats anywhere.
However, behind the scenes Ed Miliband and his team have always taken the view that the rise of UKIP was good for Labour - some at the party's HQ told my colleague Iain Watson that the willingness of Northern Tories to switch to UKIP could help them win 14 more seats in that region alone.
If they're right Labour will be able to win the next election on a national vote of not much more than 35% and won't need Mr Farage's support to move into Downing Street.
There is one other problem facing UKIP - the first past the post electoral system used for Westminster elections is very cruel to parties which amass an awful lot of votes in an awful lot of places coming a very good second or third in lots of places but first in very few.
That was the fate of the Lib Dems for a very long time but they've wised up to how to play the system. At the last general election the Greens got an MP elected in Brighton with 1% of the vote nationally whereas UKIP got none with three times as many votes.
At the next election UKIP could beat the Lib Dems in the national vote share but get a fraction of the number of MPs.
Until recently the optimists in UKIP talked of them electing a handful of MPs - Farage certainly, maybe Carswell again plus one or two more. With that level of support they'd be very unlikely to hold the balance of power. Mr Farage will not get to be Minister for Europe. The self styled People's Army would not breach the walls of power.
Maybe but maybe the seemingly ever onward rise of Mr Farage will, as he's long predicted, continue ever onward.