David Cameron is facing renewed backbench disquiet over the European Union after he tried and failed to satisfy Conservative demands for a referendum.
Conservative MPs warned that the Prime Minister had not gone far enough by declaring that he would consider calling a referendum - but not yet.
Mr Cameron was accused of offering "jam tomorrow" with his offer to go to the people once Britain's future relationship with Brussels, in the aftermath of the eurozone crisis and further EU integration, becomes clear.
He insisted that an immediate in/out referendum was not what the public wanted.
But, in an article for The Sunday Telegraph, Mr Cameron acknowledged the need to ensure the UK's position within an evolving EU has "the full-hearted support of the British people".
He stressed there would be further opportunities in the coming months and years to win back powers from Brussels and that he wanted to be able to offer voters a "real choice" in any potential referendum.
"As I have said, for me the two words 'Europe' and 'referendum' can go together, particularly if we really are proposing a change in how our country is governed, but let us get the people a real choice first."
He is expected to set out more detail about the possibility of a referendum in the autumn.
But influential eurosceptic backbencher Mark Pritchard said Tory grassroots were "fed up of aluminium guarantees" and insisted there should be a referendum during the current parliament.
"Once again, when it comes to Europe, it's always jam tomorrow. But tomorrow may never come," he said.
Nearly 100 Conservative MPs wrote to Mr Cameron recently urging him to make a legal commitment to hold a poll on the UK's relationship with the EU during the next parliament.
Tory MP John Baron, who organised the letter, told the BBC: "I welcome the fact he is now talking about a referendum, but you will notice he hasn't promised one and that he is justifying that position by suggesting now is not a good time for an in-out referendum.
"That's not what we have called for in our letter. We have simply called for a commitment to be put on the statute book in this parliament for a referendum in the next parliament."
Tory MP Peter Bone told Channel 4 News: "I think the British people will find it very difficult to believe any party leader who goes into the next election with a manifesto promise of an EU referendum, because let's face it none of them have delivered it.
"We want to see legislation in this parliament so that there would definitely be a referendum in the next parliament.
"That's what the British people want."
He added: "We just need to push a little harder and get that referendum in this parliament."
Former defence secretary Liam Fox will today warn that Britain's national interest is at risk as the Government's power is "curtailed by diktat from Brussels".
"We should not wait for EU leaders to recognise the failure of the ill-conceived euro before we set out what we want for the British people," he will say.
"Britain's destiny is not a debating issue for leaders on the Continent."
He will also say that "life outside the EU holds no terror".
"I would like to see Britain negotiate a new relationship on the basis that, if we achieved it and our future relationship was economic rather than political, we would advocate acceptance in a referendum of this new dynamic.
"If, on the other hand, others would not accede to our requests for a rebalancing in the light of the response to the euro crisis, then we would recommend rejection and potential departure from the EU," he will say.
'It is not a coincidence that some convinced euro-enthusiasts support such referendum calls, confident that a scare campaign based on false fears of political and economic isolation would win the day."
The issue also threatens to place new strains on the Tory coalition with the Liberal Democrats, who said Mr Cameron was not speaking for the Government and suggested he was responding to "internal divisions" in his party.
Lib Dem Business Secretary Vince Cable said the referendum question was "horribly irrelevant".
"Reopening a big debate about Britain being in or out the European Union and the referendum associated with it is horribly irrelevant at a time of upheaval taking place in Europe," he said.
Labour said Mr Cameron's positioning on a referendum was a "shambles" and revealed more about his "weakness" in managing his party than in his plans for a plebiscite.