A protester at a demonstration for equal rights for gay couples in Trafalgar Square on March 24, 2013
British Prime Minister David Cameron headed off another Conservative rebellion after the opposition Labour Party helped him see off a "wrecking amendment" which had threatened his gay marriage bill.
Tory MP Tim Loughton had proposed the amendment saying that if gay couples were allowed to marry, then heterosexual couples should also be able to have civil partnerships.
But lawmakers in the lower House of Commons rejected the motion by 375 votes to 70.
Instead they backed an alternative amendment tabled by Labour calling for an immediate consultation on extending civil partnerships to heterosexual couples. That passed by 391 votes to 57.
Loughton opposes same-sex marriage, and the Conservative-led government had called his proposal a "wrecking amendment". They had argued it would delay the passing of the gay marriage bill by up to two years and cost £4 billion ($6 billion, 4.7 billion euros) in pension changes.
Even if it was defeated however, some 56 Tory MPs backed his amendment.
On Sunday, Labour was reported to be considering backing the Tory the rebels to deliver a blow to Cameron's authority.
But earlier Monday, the party said it would instead back the government so that the bill, which it supports, would not be held up.
Labour leader Ed Miliband nevertheless made the most of the Conservative leader's discomfort.
Cameron's "inability to control his party must not be allowed to wreck the Equal Marriage Bill", he tweeted. "Labour's commitment unwavering," he added.
In February, when it was last debated, the bill was approved by a comfortable 225-vote majority despite the opposition of almost half of Conservative lawmakers.
Monday's deal, after five hours of fractious debate, allows the bill to proceed to the upper house of parliament, the House of Lords, where it is expected to face stiff opposition.
Lawmakers are allowed a free vote on gay marriage, meaning they are not required to follow party directions because it is considered an issue of conscience.
The vote came at a time when Cameron was already under pressure from a large section of his fractious centre-right party over his stance on a referendum on Britain's membership of the European Union.
Grassroots Conservative supporters fear that with a general election two years away, Cameron's backing for gay marriage is driving traditional Tory voters to the UK Independence Party (UKIP).
They are all the more anxious because UKIP had its best ever electoral performance last month when it made gains in local elections.
A letter signed by more than 30 current and former Conservative local party chairmen and handed to Cameron on Sunday gave a taste of the bitterness in Tory ranks.
They accused him of "treating the membership with contempt" over the issue.
"The bill could cost us the election... therefore, prime minister, for the sake of the well-being of the country and the integrity and future success of the party, we urge you not to continue with your policy of re-defining marriage," it said.
Over the weekend, a member of Cameron's inner circle fiercely denied claims that he had branded grassroot party members as "mad, swivel-eyed loons".
Party co-chairman Lord Andrew Feldman, a schoolmate of Cameron's at the elite Eton College, has strenuously denied rumours linking him with the comments and said he was considering legal action.
To try to calm the waters, Cameron issued a message to all Conservative party members on Monday praising their work .
"I am proud of what you do," he said. "And I would never have around me those who sneered or thought otherwise. We are a team, from the parish council to the local association to Parliament, and I never forget it."
Conservative backbenchers' fears over the rise of UKIP prompted around 114 Tory MPs last week to back a motion in parliament expressing regret that the coalition government's plans for the year contained no guarantee of a referendum on EU membership.
On Saturday, France became the 14th country to legalise gay marriage when Socialist President Francois Hollande signed it into law, despite fierce protests from the main opposition right-wing UMP party.