British Prime Minister David Cameron has suggested the possibilty of a future referendum on Britain's relationship with the European Union, but not on whether to stay or leave.

Mr Cameron said a vote may be needed to get the full hearted support of the British people for changes in the way they are governed.

In an article for the Sunday Telegraph, he said he did not want a definitive vote on membership now because leaving the EU would not be in Britain's best interests and a vote to stay in could hamper further attempts to change the relationship with Brussels.

Mr Cameron said he agrees with the "vast majority of the British people" who he said were not happy with the UK's relationship with the EU.

There were large amounts of EU legislation that should be scrapped, he said.

Nearly 100 Conservative MPs have written to Mr Cameron urging him to make it a legal commitment to hold a poll on the UK's relationship with the EU during the next parliament.

Foreign Secretary William Hague said there would be a "very, very powerful" case for a referendum if Europe moved towards a more federal system, as expected in response to the eurozone crisis.

But he said the government wanted to see whether it could negotiate a better relationship between the UK and Brussels, with the return of powers, before putting the matter to the British people.

Asked about the EU's moves towards closer union, Mr Hague said: "If it changes in that way and once we know whether we can get a better relationship with Europe then that is the time to make the case for a referendum or if there is a clear division between the parties to decide in a general election.

"That is the time, not now."

Mr Cameron would be setting out his position on a referendum in more detail in the autumn, Mr Hague said.