UKIP: Rochester and Strood poll 'most important for 30 years'
The UKIP leader Nigel Farage has claimed the forthcoming Rochester and Strood by-election is "the most important for more than 30 years".
He visited the constituency to meet the incumbent MP Mark Reckless, who left the Conservatives for UKIP last month.
Mr Farage said if his party wins the seat on 20 November, UKIP would be in a "very different place", as it ranks the seat as its "271st most winnable".
David Cameron has pledged to "negotiate a better deal for the UK in Europe".
The prime minister visited the Kent constituency on Thursday where he told audiences he was the only person who could deliver an in/out referendum.
Mr Farage said: "This is a very serious, important by-election. I think it's the most important in British politics in over 30 years.
"The result of this matters a lot and that's why the prime minister was saying things yesterday we haven't heard him say in the nine years he has led the Conservative Party."
If Mr Reckless wins it will be UKIP's second by-election victory following fellow Tory defector Douglas Carswell's recent success in Clacton, Essex.
He became the first UKIP candidate to be elected to Parliament.
By Louise Stewart, BBC South East Today political editor
Nigel Farage is becoming a very familiar face on the streets of Rochester and Strood.
He has made several visits here already to support the former Conservative MP Mark Reckless, whose defection to UKIP triggered this by-election.
He believes if UKIP can win here - number 271 on their list of most winnable seats - the Tories will be seriously concerned about the challenge UKIP poses in next year's general election.
Yesterday, David Cameron made his first of several visits - he is expected to come four more times before polling day and expects his cabinet colleagues to do the same.
Earlier in the week, Labour's shadow equalities minister Gloria de Piero lent her support to the party's candidate. So far no big hitting Liberal Democrats have taken to the campaign trail here and the party looks likely to be punished at the polls - perhaps losing their deposit again.
Mr Farage said the by-election was the most crucial since Roy Jenkins was elected for the Social Democratic Party in Glasgow Hillhead in 1982.
The Conservatives said they are holding an open primary to select a candidate for the by-election.
The full list of candidates announced so far can be found here.