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.

Mrs Miller had argued that extending civil partnerships to opposite-sex couples - supported in principle by many backers of gay marriage - would cause significant delays and costs.

She put forward plans for a review after gay marriage had been operating for five years but then accepted Labour demands for an immediate referendum as the price of the party's crucial support.

A series of other amendments tabled by Tory opponents of the reforms were also defeated - including one which would have given registrars who objected to same-sex unions the right to refuse to conduct marriages which was backed by 150 MPs, including 122 Conservatives.