UK may hold EU referendum, PM says

But he cautioned against an in/out referendum. "Leaving would not be in our country’s best interests" while a British vote to stay in the union would mean that subsequent attempts to change London's relations with Brussels would run into cries that the "British people had already spoken."

"What I believe the vast majority of the British people want is to make changes to our relationship."

Elaborating on Cameron's statements which British media have interpreted as change in tone if not in policy, foreign secretary William Hague said:

“What the Prime Minister is saying is that the time to decide on a referendum or a general election on our relationship with Europe is when we know how Europe is going to develop over the coming months and years to the eurozone crisis, and when we know whether we can get that better relationship."

But Cameron's latest wait-and-see statement has riled his backbench eurosceptics, who see the eurozone's steps to create a political and fiscal union as the perfect reason for the UK to take a harder line.

Liam Fox, a former defence secretary and influential eurosceptic, is to give a speech on Monday (2 July), in which he will agree that an in/out referendum would be a "tactical" mistake but that London should renegotiate its membership terms to be based on an economic or monetary union.

If it does not get its way then it should have referendum, and the government would recommend withdrawal from the EU.

"Life outside the EU holds no terror," he wrote in the Sunday Telegraph.

While Cameron has managed to keep the notoriously lukewarm British relationship with the EU from swamping his premiership, the changing nature of the eurozone debate has made this more challenging.

As a non-euro member, London is fretting that further integrative steps by single currency states could affect its prized financial services sector and the single market, the part of the EU for which it feels most affection.

Traditional eurosceptics meanwhile see the referendum as long due, with the previous labour government having promised a referendum on the EU constitution, the France- and Netherlands-rejected predecessor to the current and similar Lisbon Treaty.