Mr Hague this morning insisted the Conservative Party has not changed its position.

"We want to have the chance to find out whether we can have a better relationship with Europe," he told the BBC's Andrew Marr Show. "We want people to have their say when they have a real choice in front of us.

"The time to decide in a referendum is when we know how Europe's going to develop and when we know whether we're going to get a better relationship."

Douglas Alexander, the shadow foreign secretary, said Goverment policy was "confused".

He suggested the Prime Minister is doing more to manage his own eurosceptic backbenchers than act in the interest of the UK.

More than 100 Conservative MPs wrote to Mr Cameron last week demanding that Britain re-negotiates its relationship with the EU.

Writing in the Sunday Telegraph, Mr Cameron says that Britain is in danger of getting swamped by EU legislation and bureaucracy which he would like to see scrapped. He makes clear for the first time that changes will need the “full-hearted support of the British people” down the line and adds: “For me the two words 'Europe’ and 'referendum’ can go together.”

Mr Cameron’s landmark move comes as Liam Fox, the former defence secretary, prepares to up the stakes by calling for an immediate renegotiation of Britain’s relationship with the EU. If other member states fail to back this solution, Dr Fox believes, there should be a referendum with the government recommending pulling the UK out of the EU.