Existing EU set-up 'unacceptable', says Cameron

But he gave his strongest suggestion yet that he would support a British exit if renegotiation efforts were unsuccessful.

"The problem with the status quo is I don't think that the status quo in the EU is acceptable today," Mr Cameron said.

"I want to change it and having changed it I then want to ask the British people a very simple in/out question."

Speaking in Washington ahead of talks with US president Barack Obama, Mr Cameron was asked if he was "comfortable" with yesterday's interventions by Education Secretary Michael Gove and Defence Secretary Philip Hammond.

"There's not going to be a referendum tomorrow, there is going to be a referendum before the end of 2017," the Prime Minister said.Mr Cameron said "the whole of the Conservative Party" was signed up to his policy of renegotiating and then staging a national poll.

He also made an appeal for Eurosceptic Tories to focus on winning the general election in two years' time.

"We are the only mainstream party making this offer to the electorate at the next general election," he said.

Some 53 MPs have now signed the Commons amendment criticising the absence of a referendum Bill in the Queen's Speech, including 50 Tories and three from Labour - Kelvin Hopkins, John Cryer and Kate Hoey.

But eurosceptic backbencher Peter Bone, one of those who tabled the motion, predicted that "most" Conservative MPs will support it when it comes to a vote in the Commons, adding that he hoped ministers would be allowed to join them.

Mr Bone said: "The amendment we have put down regretting that there is no EU Referendum Bill is of course the Prime Minister's policy. I am sure that in America, he is toasting what I and a number of other colleagues have done, and I'm sure that if he wasn't in America he would be supporting the amendment.

"The reason there is no EU Referendum Bill is that the pesky Liberal Democrats are blocking it in the coalition. They are such a small minority party - far smaller than Nigel (Farage)'s party. Why should we take any interest in them?

"Most Conservative MPs will vote for it. By the time we get to Wednesday, I hope the ministers will be allowed to vote for it."

Voting against an EU Referendum Bill would be "political suicide" for Labour because it would send a signal to voters that the party would not give them a referendum, said Mr Bone.

But Labour Europe spokeswoman Emma Reynolds insisted that Labour had not ruled out a referendum for all time.

"We are not in favour of a referendum now and not in favour of a referendum at some arbitrary point in the future," said Ms Reynolds. "However, in foreign policy it would be unwise to rule something out forever and we would have a referendum if there were a transfer of power from Westminster to Brussels."

She added: "It beggars belief that the Prime Minister, who is leader of the Government, is almost encouraging - or apparently 'relaxed' about - his own MPs voting against his Government's programme."

Mr Farage claimed that it was "almost guaranteed" that Labour would eventually switch to backing a referendum, and said that leader Ed Miliband's speech on Europe last weekend had made it easier for Ukip to woo Labour voters.

He claimed that one Labour constituency party and a number of Conservative constituency associations were considering the possibility of candidates running on a joint "Conservative/Ukip" or "Labour/Ukip" ticket in the 2015 election.

"I am open-minded on a seat-by-seat basis to talk to people about co-operation," Mr Farage said, though he ruled out a formal party-wide agreement so long as Mr Cameron is Tory leader.

"There is no doubt that there are Tory associations, and one Labour I know of, who are saying that there is a provision that a candidate can have the endorsement of two parties and there are associations out there who want to do that."

Micahel Gove and Philip Hammond both stressed yesterday that they supported Mr Cameron's bid to renegotiate and stage a referendum before 2018.

But asked about reports last year that he told friends he would vote No if there was a referendum now, Mr Gove said: "Yes. I'm not happy with our position with the European Union. But my preference is for a change in Britain's relationship."

Mr Hammond said later: "If the choice is between a European Union written exactly as it is today and not being a part of that then I have to say that I'm on the side of the argument that Michael Gove has put forward."

Mr Cameron will be in the US for an expected vote on a Commons amendment criticising the absence of a referendum Bill in the Queen's Speech.

Up to 100 Conservatives are expected to back the amendment on Wednesday - although Labour and Liberal Democrat opposition means it is certain to fail.

Downing Street confirmed today that Conservative ministers have been told that they can abstain.

But in a break from normal practice, Tory parliamentary private secretaries (PPS) will be allowed to keep their jobs if they vote for the rebel amendment.

Usually, if PPSs - who are MPs acting as unpaid aides to ministers in Parliament - vote against Government policy, they must quit their posts or face the sack.

Nigel Farage accused Mr Cameron of trying to obscure the truth of what would be involved if Britain was to leave the EU.

He said that, under the terms of Lisbon Treaty, a country wishing to withdraw had to action Article 50 of the treaty, which then provided for a two-year "period of grace" while negotiations took place.

"He isn't haggling, he is wriggling," Mr Farage said.

"The Prime Minister is obscuring the truth. One can only imagine it is to fool his own backbenchers because it doesn't fool our friends on the Continent."

Shadow foreign secretary Douglas Alexander defended Labour's position of refusing to commit itself now to a referendum in 2017, while not ruling out the possibility of offering a public vote on Europe at some point in the future.

"Labour's position is straightforward," Mr Alexander said. "The right choice for Britain now is to maintain economic stability and try to secure growth.

"We don't honestly believe that the biggest problem facing Britain today is Europe. The biggest problem is the economy. Therefore, every judgment we make - for example in relation to our policy towards Europe - should reflect the concerns that we have about the need for economic stability.

"If a policy choice - like that suggested by the Prime Minister - adds to instability and threatens jobs, then we don't believe that to be in the national interest."

Another Conservative former Cabinet minister today said he would vote to take Britain out of the EU.

Lord Forsyth, who served as Scotland secretary under John Major from 1995-97, told BBC2's Daily Politics: "I certainly want us out of the EU if there was a referendum tomorrow, not because we are leaving the EU but because the EU is leaving us.

"It is clearly going to go down the past of further economic integration and that is not going to make Europe competitive and we can see the misery that's being caused in countries like Spain... We can't go down that track."

Lord Forsyth said Mr Cameron was "wrong" to think he can renegotiate Britain's membership with the other 26 EU members, adding: "David Cameron is thinking he can persuade the golf club to play tennis, and his negotiating position is impossible because he is saying, 'If I don't succeed, I will continue to play golf.'"