David Cameron looks set for a by-election humiliation at the hands of Ukip following former MP Douglas Carswell's defection, according to an opinion poll.
Mr Carswell's decision to join Nigel Farage's party and trigger a by-election shocked Westminster and the poll of voters in the Clacton seat predicting a massive 44 point lead for Ukip will add to the prime minister's discomfort.
The Survation study for the Mail on Sunday put Ukip on 64%, with Mr Carswell's former party on 20%, Labour on 13% and the Lib Dems on 2%.
Ukip have a huge 44 point lead in the Clacton by-election, the poll said
More than half of those polled favoured quitting the European Union, with 54% supporting a British exit and 26% opposed to cutting ties to Brussels.
In a sign of Mr Carswell's popularity in the seat, more than a third (34%) of those indicating they would vote Ukip said it was because they liked their former Conservative MP, while 57% said it was because they liked Ukip and 9% said it would be a protest vote.
Among Tory voters, almost half (49%) said Mr Carswell was a hero despite his defection, with just 17% saying he was a traitor.
The poll of 700 voters - smaller than the samples typically used in nationwide polling - was carried out within hours of Mr Carswell's defection.
Mr Cameron has dismissed Mr Carswell's decision as "bizarre" because he had promised a referendum on the UK's membership of the EU by the end of 2017.
David Cameron has called Carswell's decision to defect 'bizarre'
His plan to renegotiate the UK's relationship with Brussels was given a major boost by the new president of the European Council.
Donald Tusk, who will give up his job as Polish prime minister to take the role, singled out the UK's agenda as an area where he wants to make progress.
He said he "could not imagine" the EU without Britain as a member - insisting it would be possible to "reach an agreement" on issues such as freedom of movement of labour.
At a press conference after his appointment was finalised by fellow European leaders in Brussels, Mr Tusk said he wanted to "emphasise that the EU, and me personally, will take on the concerns voiced by the UK".
He said: "I am talking about the UK because I am sure that the future of the EU is not about making it smaller, about contraction.
"No reasonable person can imagine the EU without the UK. I cannot imagine it myself.
"I have talked about it with David Cameron. He put forward many proposals for reforms and I am sure with a reasonable framework of politicians we can reach an agreement.
"We can strive to eliminate various barriers - freedom of movement of workers, for example."
The strong words from Mr Tusk - who described the prospect of a British exit as a "dark scenario" - suggests he could be an important ally.
However, Downing Street believe he is focused on curbing abuses of freedom of movement, such as inappropriate access to welfare, rather than fundamental changes to the principle.
According to another translation the president-elect - who was unanimously backed by EU leaders - also said: "Many of the suggestions put forward for EU reform are sensible, we can work together to eliminate any welfare abuse by EU migrants."
Speaking to journalists as he left the EU summit in Brussels, Mr Cameron said: "I'm delighted obviously with what Donald Tusk has said about the importance of reform in the EU and addressing the concern that Britain has in the EU.
"I look forward to working with him in the months and the years ahead."