British Prime Minister David Cameron's Conservative party bowed to pressure from euroskeptic lawmakers on Tuesday and published a bill enshrining in law a promise to hold a referendum on the nation's membership of the European Union.

The unexpected move, which Cameron had been resisting for months, came the day before at least 67 Conservative MPs were expected to vote for a parliamentary motion condemning the coalition government's European policy.

The announcement also came just hours after Cameron, on a trip to Washington, secured the public support of US President Barack Obama for his plan to renegotiate Britain's terms of membership with Brussels before putting it to a national vote by 2017.

The Conservatives' bill would turn into law the prime minister's promise to hold a referendum, which is contingent on the party winning re-election in 2015.

But it is a highly unusual move because it has been published by the party, not the coalition government, and the bill will rely on an individual Tory member of parliament guiding it through parliament.

Foreign Secretary William Hague, the most senior euroskeptic Tory, acknowledged the bill had almost no chance of becoming law because of opposition from the Liberal Democrats, the pro-European party which shares power in the Tory-led coalition.

"But it means there can be a debate in the House of Commons on our policy, it means there can be a vote in the House of Commons," Hague said.

"When all the dust settles on the speculation about this, one thing will be very clear. ... The Conservative Party is very much behind and committed to this policy."

Agence France-Presse