Oliver Letwin, the senior Conservative charged with helping to draw up the party's general election manifesto, has said he will vote to leave the European Union if David Cameron fails to win enough powers back from Brussels.
The Cabinet Office minister, who is close to the prime minister, also said the new European Commission, headed by Jean-Claude Juncker, was the "Commission from heaven".
Cameron has pledged that should he be returned to Downing Street at the election in six months time, he will give voters an in/out referendum in 2017. Before then he hopes to renegotiate for the UK a looser relationship with the EU. The public would be asked to approve that new deal. However the specifics of what that new relationship would look like are unclear.
Speaking to an audience of students at University College London on Tuesday evening, Letwin, who wrote the 2010 Tory manifesto, said he would be happy for the UK to be part of an "outer-rim" of EU states that was part of a "free-trade zone". He indicated he wanted to see substantial powers over borders and justice repatriated.
"If we can achieve that in negotiations then I shall certainly be supporting remaining within it in the referendum in 2017," he said. "We have to have that referendum. We have to put to the British people that question.
"We will see whether what we are able to negotiate is acceptable. I think they deserve that choice. If we don’t get the sort of position that I was describing then I wouldn't want to recommend staying, I would want to recommend leaving. It's better than being absorbed into a United States of Europe."
Letwin added that he thought it was more likely than not that Cameron would be able to get the deal he wanted, but it was not definitely achievable. "Certainly not 100%. I can’t guarantee it. Better than 50/50," he said. "I don’t know what the chances are, but I think they are more like 80/20 than 20/80."
The minister for government policy said he believed other EU states, including Germany, recognised the domestic political pressure the government was under."[There is a] very strong chance they will cut us enough slack in negotiations to enable us to put to the British people [something] that would stand a chance of winning," he said.
The latest YouGov poll showed voters were split on the UK's membership of the EU, with 39% of people saying they would vote to stay and 39% saying they would vote to leave.
However the survey found that if Cameron managed to secure a renegotiation and recommended a yes vote, 58% would vote to stay, 24% would vote to leave.
Cameron has dodged questions about whether he would recommend Britain leave the EU should his attempt at renegotiation fall short of what he wants. Challenged by Ed Miliband at prime minister's questions earlier this month, the prime minister simply replied: "I think Britain is better off in a reformed European Union".
Letwin's comments show how a failure to satisfy eurosceptics could open up deep divisions at the top of the Conservative Party at the time of any referendum.
In June, Cameron failed to prevent Jean Claude-Juncker from becoming the new president of the European Commission. But Letwin said on Tuesday that senior Conservatives were actually quite pleased with how things had turned out.
"The ultimate effect was absolutely brilliant, much better than we could have possibly have guessed," he said. "He has turned out he is much more reasonable than we thought he might be. Partly because he knows he has to be because we would get very cross with him, secondly he felt under pressure to create a Commission which we and others who felt like us were willing to accept."
Letwin said the appointment of Britain's Lord Hill as financial services commissioner was a major victory. He added that "all the other really important portfolios" in the Commission went to the people that the UK wanted, which came to the "complete astonishment" of No.10.
He added: "We created the Commission from heaven from our point of view. We didn't know that would be the effect. It's where we got to."
Cameron is likely to come under further pressure over the EU and immigration this week when, if as expected, Ukip win the Rochester by-election triggered by Tory defector Mark Reckless.Suggest a correction