Conservative grandee John Redwood has dismissed the "so-called" eight Tory MPs allegedly considering defection to Ukip as "figments of Ukip's imagination".
"Dream on Ukip," the eurosceptic MP for Wokingham and former Wales Secretary told Radio 4's Today programme.
"I treasure the words of Mr Carswell which he was speaking yesterday. He said that we need to deliver an in-out referendum, he said it would only happen if David Cameron was prime minister," Mr Redwood said.
"He said we must do nothing to make the prospect of a referendum less likely. He was super-loyal until yesterday."
Ukip leader Nigel Farage and his new recruit Douglas Carswell are in Clacton as the pair plan a completely unexpected by-election campaign.
They are visiting the seat after Mr Carswell's bombshell decision to switch parties and quit the Commons to re-stand under the Ukip banner.
The rebel Conservative MP Douglas Carswell delivered a double blow to his party today - a shock defection to Ukip and he has forced a by-election in Essex which many believe the Tories are likely to lose.
The deeply Euro-sceptic Mr Carswell, who is the MP for Clacton, was unveiled as Ukip's newest recruit in a press conference in London. He said he was defecting from the Tories because Mr Cameron was not serious enough about the change needed in Britain's relationship with Europe.
He will resign as an MP when Parliament returns next week, forcing a by-election which could see him returned as Ukip's first ever elected member of parliament.
Click below to watch a full interview with MP Douglas Carswell:
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Prime Minister David Cameron has described Tory MP Douglas Carswell's defection to UKIP as "deeply regrettable" and "self-defeating".
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William Hague has said Douglas Carswell's decision to defect to Ukip is "totally counter-productive" because only the Conservatives can offer the public a choice on EU membership.
The Leader of the Commons said: "It's a totally counterproductive thing to do, of course, because the only chance of real change in Europe, the only chance of having a referendum where people can decide to say in the EU or leave the EU is having a Conservative government."
Backbench Tory MP Mark Pritchard agreed with Mr Hague, saying Mr Carswell had made an "error of judgment" that would end up helping Labour in the 2015 general election.
Defecting Conservative MP Douglas Carswell says he want to "shake up" the Westminster "clique" with his move to Ukip.
Carswell said the Conservatives' failure to take a stand against the European Union was at the heart of his decision.
ITV News Political Correspondent Libby Wiener reports:
Ed Miliband has tweeted that Douglas Carswell's defection show the Conservatives are "too divided to stand up for hard-working families".
Douglas Carswell’s defection is not just a blow to David Cameron. It shows the Tory Party too divided to stand up for hard-working families
A senior Tory in Douglas Carswell's Clacton constituency has said news of his defection to Ukip has come as a "bolt from the blue".
Mick Page, the leader of Tendring District Council, which covers Clacton said: "That's come as a shock - a bolt from the blue."
Speaking to the Press Association he added: "We always thought he was a Conservative very much against Europe but we thought he would work within the party to achieve his aims. As far as I'm aware the Conservative association had no warning of this."