The legalisation of gay marriage is poised to be approved by MPs after surviving a Tory backbench bid to derail it.
Some 56 Conservative backbenchers - half the number predicted - backed an amendment the Government warned could fatally delay the reform.
Eight Labour MPs, three Liberal Democrats and three SDLP members joined the Tory critics in the voting lobbies. But the move to extend civil partnerships to heterosexual couples was easily defeated in a free vote by a large majority of 370.
An embarrassing reverse was avoided after the Government accepted Labour calls for an immediate review of civil partnerships instead. But if it clears its final stages in the Commons, the Marriage (Same Sex Couples) Bill still faces stiff resistance in the House of Lords.
Conservative ex-minister Tim Loughton accused ministers of doing a "grubby deal" with Labour to see off his amendment and said the battle would continue in the upper chamber. And the Conservative leadership remains under fire from many senior party members vehemently opposed to the measure.
On Monday night, one councillor accused ministers of showing "clear contempt for the deeply-held views of Conservative supporters" and fuelling an exodus to the UK Independence Party. But Culture Secretary Maria Miller defended the Government's tactics insisting there was "overwhelming support" for the change, including among significant numbers in her own party.
In an early sign of the rough ride the Bill is likely to have in the House of Lords, Conservative former Cabinet minister Lord Tebbit accused the Government of failing to think through the implications of same-sex marriage for issues such as the succession to the throne.
Lord Tebbit told the Big Issue magazine: "The Government discussed it for 20 minutes on the morning of its announcement. They'd done no work on it beforehand. I said to a minister I know: 'Have you thought this through? Because you're doing the law of succession, too'.
"When we have a queen who is a lesbian and she marries another lady and then decides she would like to have a child and someone donates sperm and she gives birth to a child, is that child heir to the throne? It's like one of my colleagues said: We've got to make these same-sex marriages available to all.
"It would lift my worries about inheritance tax because maybe I'd be allowed to marry my son. Why not? Why shouldn't a mother marry her daughter? Why shouldn't two elderly sisters living together marry each other?"