Nigel Farage's UK Independence Party (Ukip) is on course for further success in next year's European elections, according to a new poll.
The survey found that 27% of those certain to vote in the 2014 contest would support Ukip, with Labour on 23% and the Tories on 21%.
The rise of Mr Farage's party has caused major headaches for the Conservatives, and the ComRes study for the Open Europe think-tank found that almost two-fifths (39%) of those who voted Tory in 2010 would back Ukip if the European election was held now.
In a general election, the poll suggested Labour would take 37% of the votes, an 11-point lead over the Conservatives on 26%, with Ukip on 20% and the Liberal Democrats on 9%.
But there was some good news for David Cameron, with widespread support for his policy of renegotiating the UK's relationship with Brussels before putting the new settlement to a public vote by the end of 2017.
If a referendum on Britain's membership of the EU were held now, 37% say that they would vote to remain in the EU compared to 41% that say they would vote to leave. But, if there was a significant return of powers to Westminster followed by a referendum, 47% would vote to stay in the EU, while 32% would still vote to leave.
The Prime Minister was rated as the party leader most likely to succeed in negotiating a better deal with 29% backing him to win back powers, with Ed Miliband on 14%, Mr Farage on 12% and Nick Clegg on 4%.
Open Europe's director, Mats Persson, said: "Whilst the Conservatives may be heading for a perfect storm in the EU elections, their overarching goal of a renegotiated position for the UK in the EU still enjoys substantial support from across the political spectrum.
"Most voters would clearly prefer to stay in the EU but on new membership terms, over withdrawing altogether. However, unless a new relationship can be negotiated, the UK electorate could well vote to leave the EU - which should also be a wake-up call for Labour and Lib Dems."
"It's rather surprising that Mr Cameron, despite everything, is still the most trusted party leader to negotiate a better deal for the UK in Europe. However, it's obvious that all parties suffer from a major credibility deficit on EU issues. For this exact reason, Mr Cameron must press ahead with a robust reform agenda now. Waiting until 2015 will risk losing the public support he still enjoys."