The legalisation of gay marriage is poised for approval by MPs on Tuesday after David Cameron headed off another Conservative rebellion.
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 MPs 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 Tuesday, MPs were scheduled to continue debating the bill at report stage before a third reading at around 7pm. It will then go to the House of Lords for further scrutiny after the half-term recess, where it is expected to receive significant opposition from the bishops.
Labour leader Ed Miliband made the most on Monday 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.
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 .
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.