Prime Minister David Cameron faces a showdown in parliament with eurosceptics on Wednesday over his plans for a referendum on Britain's membership of the European Union.
Disgruntled backbenchers from Cameron's Conservative party have tabled a parliamentary motion expressing "regret" that the coalition government has failed to enshrine in law the promise to hold an in/out referendum.
They are angry that the promise was not included in last week's Queen's Speech, in which the government set out its programme for the year.
Parliamentary speaker John Bercow has approved the backbenchers' motion and has allowed it to be the subject of a vote on Wednesday.
Cameron, who will miss the vote because he is visiting the United States, has insisted he is "profoundly relaxed" about it despite the prospect that scores of Conservative backbenchers could back the amendment.
The vote is purely symbolic, because the motion is certain to be defeated.
But it is a sign of the anger among Conservative lawmakers is growing over the issue of Britain's EU membership, which has long split the party.
Cameron tried to quell the rebellious mood in his party on Tuesday by publishing a draft bill revealing the wording of a referendum.
Cameron denied that he had been panicked into rushing through the proposed legislation, which would legally enshrine his commitment to hold a vote on Britain's place in the 27-nation bloc by December 31, 2017.
The leader of the main opposition Labour Party, Ed Miliband, said Cameron had "completely lost control" of his party on the issue.
Cameron argues that he wants to renegotiate the conditions of Britain's membership of the EU before putting the question to the people in a referendum.
He insisted he had always accepted the need to do whatever was possible to strengthen his pledge to hold an in/out referendum before the end of 2017.
"People need to know that this is a serious pledge that they can bank," he said.
Under the provisions of the one-page draft EU (Referendum) Bill voters would be asked the question: "Do you think that the United Kingdom should remain a member of the European Union?"
Labour opposes legislating now for a referendum in four years' time, although it too is divided over Europe.
The vast majority of Labour lawmakers will oppose the amendment on Wednesday, although a small number have signed up to it.
A Guardian/ICM poll published this week found 35 percent of Britons favoured an immediate referendum, while 43 percent said they would vote to leave the EU and 40 percent said they wanted to stay in.