David Cameron has said he would never campaign for Britain to leave the European Union, in a move that will be sure to upset eurosceptic Tory MPs.
In an interview with the Daily Telegraph, the prime minister said he wanted Britain to be a "winning" nation and that it could not do that if it withdrew from the union. “I think it would be bad for Britain,” he said.
“When I look at what is in our national interest, we are not some country that looks in on ourself or retreats from the world.
"Britain’s interest – trading a vast share of our GDP – is to be in those markets. Not just buying, selling, investing, receiving investment but also helping to write the rules. If we were outside, we wouldn’t be able to do that.”
He added: “It comes back to this, who are going to be the winning nations for the 21st century? If your vision of Britain was that we should just withdraw and become a sort of greater Switzerland, I think that would be a complete denial of our national interests.”
Cameron's comments were criticised by backbench Tory MP Douglas Carswell, who told The Huffington Post that the prime minister had made a "basic" negotiating error as the Germans and the French would now know any threat made by the UK that it would leave the EU was not genuine.
The prime minister's reference to Switzerland echos the words of European Commission president Jose Manuel Barroso, who recently warned British eurosceptics that the UK would be reduced to the stature of a "Noway or Switzerland" it separated itself from the EU.
Under pressure from his own backbenchers, Cameron has indicated that he would be willing to hold a referendum on Britain's relationship with the EU following the 2015 general election.
However he has ruled out an immediate in/out vote, much to the frustration of the eurosceptic wing of his party.
At the start of the month nearly 100 Conservative MPs called for a poll during the next Parliament, and urged Cameron to make it a legal commitment to hold a vote on the UK's relationship with the EU.
In October 2011 81 Tory MPs rebelled against the prime minister when they defied the government to vote in favour of holding an immediate referendum.
It has been suggested that Britain should attempt to renegotiate its relationship with Brussels and demand the repatriation of powers to Westminster.
Former defence secretary Liam Fox has said said Britain should negotiate a "new relationship" with the EU based on "economic rather than political considerations" followed by a referendum to allow voters to agree to the new set up.
And he said if other EU nations were not willing to accept this then there should be a referendum on whether to leave the EU all together.
However Cameron has further incensed critics of the EU with his comments in today's Telegraph, amid concerns he had shown other leaders including German chancellor Angela Merkel his cards.
Carswell, who favours withdrawal from the union, said the prime minister had made a "basic" negotiating error that even "ordinary people" would understand.
"If you start from the premise that you're going to stay in at any price, you're going to get a bad deal," he said. " Good luck with those negotiations."
"If the prime minster was serious about renegotiation then why on Earth has he said he is going to accept EU membership on any terms, it doesn't make sense.
"If you're going to buy a second-hand car and you're going to tell the guy you're going to have to buy a car that day, are you likely to get a good a deal?"
Carswell said he found it "difficult to believe" that the prime minister would now be able to secure the sort of deal that many want and predicted this would be reflected in the next set of polls.
"I think this will hit our base, our core vote, hard," he said. "When the prime minister vetoed a new treaty at the end of last year we shot up six points in the polls, I wouldn't be surprised if the next set of polls show us on or below 30%."
However senior Tory Bernard Jenkin said on Twitter that the prime minister could be in a stronger negotiating position as he was effectively telling other EU leaders: "Don't think you can get rid of me."
Earlier this month William Hague announced that the government is to conduct a review of how EU powers impact the UK, however he denied it was laying the groundwork for a referendum.
"This work will help inform decisions on Britain's future path in Europe. It is not a consultation about disengaging or withdrawing from the EU," he said.