British Prime Minister David Cameron is facing a revolt by party members opposed to same-sex marriage.

London - British Prime Minister David Cameron's cabinet allies launched a last-minute push to persuade their Conservative Party colleagues to back his plans for gay marriage at a vote in parliament Tuesday.

Cameron has championed the drive to allow same-sex couples to marry but faces the potential embarrassment of seeing half his party's lawmakers opposing him in the vote.

While the prime minister faces an uncomfortable evening, the outcome of the vote is not in question because the draft legislation has overwhelming support from the opposition Labour Party.

A vote in favour would put Britain well on track to be the 11th country to allow gay couples to marry. Same-sex couples in Britain have had the right to live in civil partnerships since 2005.

The push to win over those Conservatives still bitterly opposed to gay marriage was led by three senior party members Ä finance minister George Osborne, foreign minister William Hague and interior minister Theresa May.

In a letter to the Daily Telegraph, they said “attitudes to gay people have changed” and same-sex marriage was “the right thing to do at the right time”.

There were signs that some of the Tory waverers were falling into line. Even Chris Grayling, a right-wing MP who once defended the right of a bed and breakfast proprietor to refuse to admit gay couples, said he would back the legislation.

Grayling said in an interview with the gay magazine Attitude that the legislation was “a sensible next step” in the evolution of social attitudes.

Culture Secretary Maria Miller, the minister responsible for the legislation, insisted there was “significant support” for the legislation from Conservative activists.

“I would point out that today not only have we had a letter from the home secretary, the chancellor and the foreign secretary in the papers, but also significant support, again, in the letters of the papers from some of our key activists around the country,” she told BBC TV.

“I don't think it is quite as cut and dried as you suggest. Yes, there is a difference of opinion and yes, some people have very principled religious beliefs on this issue, but there is clear support within my party and indeed within the other major parties.”

Cameron has promised lawmakers a free vote on the proposed legislation in the House of Commons on Tuesday, meaning that party managers will not try to influence their choice.

But many backbench Conservative lawmakers opposed to gay marriage were unmoved by the pleas for them to fall into line.

One, Brian Binley, warned the legislation posed the greatest risk to the stability of society since the “social tsunami of the 1960s”.

“This bill risks institutionalising division whilst further undermining marriage in the eyes of many of those of us who see it as something greater than a mere legal device.

“That could cause a most grievous injury to social cohesion, and weaken Ä rather than strengthen Ä that institution which has served humanity so well for generations,” he wrote on his blog.

The proposals are opposed by the Church of England and its new Archbishop of Canterbury Justin Welby, but the legislation bans the “official” churches from offering gay marriage.

If the bill is passed by the House of Commons, it must next be scrutinised by a committee of lawmakers and then go before the upper chamber the House of Lords before becoming law.

While a majority of people in Britain back gay marriage, polls show that Cameron's strong support for the issue could cost his party more votes that it wins at the next general election in 2015.

More than a third, 34 percent, said it made the Conservatives less attractive to them as voters, compared to 15 percent who said it made the party more appealing, according to the ComRes survey for ITV News.

The poll of 2,050 people also showed less support than previous polls for same-sex marriage.

Some 42 percent were in favour, against 40 percent who were not.

The issue has not however sparked the impassioned protests seen in France, where the National Assembly on Saturday overwhelmingly approved a key piece of legislation that will allow homosexual couples to marry and adopt children. - Sapa-AFP