The British people should be given a say on any "fresh settlement" in the European Union in the wake of the eurozone crisis, Foreign Secretary William Hague said.
Voters could be given a chance to express their views either in a referendum or at a general election.
But speaking on the eve of the Conservative Party conference in Birmingham, he indicated that a straight in-or-out referendum demanded by many Tory MPs was unlikely.
"There's likely to come the time that a fresh settlement will require fresh consent either in a general election or a referendum," he said.
Asked whether the next general election would effectively serve as a referendum on Britain's membership of the EU, he said: "On that you'll obviously have to wait for our manifesto for the next election.
"The Prime Minister has said that he will speak, that he will make a speech on that in the coming months. So I think there will be more answers to that at that time."