Tories have accused David Cameron of admitting defeat to Ukip in next month’s crunch by-election where the party is on course to win a second Commons seat.

The warning came after Mr Cameron announced that a bitterly divisive vote on whether to keep the European Arrest Warrant would be held before the contest in Rochester, Kent not afterwards.

It is predicted that up to 100 Tory backbenchers will rebel against the Government, which would be the biggest rebellion yet and a major blow to Mr Cameron’s authority.

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Polls suggest Mark Reckless is on course to win the Rochester and Strood by-election on November 20

In the Commons yesterday, Ed Miliband accused the Prime Minister of delaying the vote because he was ‘paralysed by fear’ of Ukip winning the Kent seat. The polls suggest defector Mark Reckless is on course to win it on November 20.

But Mr Cameron surprised MPs by announcing: ‘We are going to have a vote, we are going to have it before the Rochester by-election. Your questions have just collapsed.’

MPs expressed surprise at the decision to risk a major revolt just days before a by-election the Conservatives had promised to ‘throw the kitchen sink at’ in terms of money and resources.

One senior Tory said: ‘It is hard to understand the timing of it. I assume they think it will bully some people into falling into line, which is not entirely proper since this is a really serious policy.

‘I don’t think it will work though – they are still looking at a very sizeable rebellion. Or they have written off the Rochester by-election, which is the general view. People don’t like being blamed for by-election failures, so they don’t want to hold the vote afterwards when MPs will be feeling really free.’

David Cameron, pictured with his party's candidate for Rochester Kelly Tolhurst, has been accused of admitting defeat to Ukip in next month’s crunch by-election

Ukip have commanding 13-point lead in Rochester and Strood, according to the latest poll by ComRes last week. They are on course to win 43pc of the vote, to just 30pc for the Conservatives.

However a spokesman for the Conservatives said the vote on the arrest warrant was being held as a soon as possible because it is an ‘important issue of security’ and the idea they had given up on the by-election was ‘complete fiction’.

Ken Clarke weighed in last night to warn the Prime Minister not to give in to Ukip’s ‘prejudiced’ message on immigration and Europe – which he said would only help Nigel Farage’s party.

After a Prime Minister’s Questions session dominated by immigration, the pro-Europe former chancellor told BBC News: ‘If we make it sound as if we think Ukip are correct in what they say on immigration and Europe and so on, then Ukip obviously are going to do rather well.

‘Of course there is public concern about these things, but the factual basis for the Ukip arguments is absolute nonsense.

In the Commons yesterday, Ed Miliband, pictured on the campaign trail in Rochester, accused the Prime Minister of being 'paralysed by fear' of Ukip winning the Kent seat

Ukip have commanding 13-point lead in Rochester and Strood, according to the latest poll by ComRes, and look likely to win the party's second seat in the Commons

‘It isn’t true that low pay, our health service problems, house prices, are caused by foreigners and immigrants and the European Union…and I really very much hope that the inhabitants of Rochester and Strood stand up to this rather prejudiced nonsense.’

Mr Clarke said it would be an ‘outrage’ if fugitives from justice were freed because Britain ‘had given in to Ukip’ by leaving the arrest warrant, which he said was essential to modern crime-fighting

Britain has opted out of 130 justice and home affairs powers imposed by the EU in 2001. The government has until December 1 to opt back to 35 of them which ministers say are in the national interest.

The most controversial of these is the European Arrest Warrant, which ministers say is vital to catch international organised criminals such as drug traffickers, terrorists and paedophiles across borders.

But dozens of Tory backbenchers disagree. Graham Brady, chairman of the influential 1922 committee of Tory backbenchers said he would vote against it as a ‘fundamental point of principle’ because justice matters ‘should be decided by British parliament and the British courts.’

Mr Miliband asked the Prime Minister yesterday why he was delaying a vote on ‘a vital tool that has helped to bring murderers, rapists and paedophiles to justice’.

Mr Cameron insisted the delay in holding the vote was the fault of the Spanish government which is holding up the negotiations.

He said: ‘I’m not delaying having a vote on it. We need, in order to have a vote on it, the small matter of a negotiation to take place within Europe which up to now the Spanish have been blocking. I think the Spanish will shortly remove their block.’

The Prime minister said the arrest warrant was an ‘important action to keep Britain safe’ and added that it had been reformed so people can longer be extradited for something that isn’t a crime in Britain and judges can reject them.