Moves to legalise gay marriage cleared a crucial parliamentary hurdle as it emerged that civil partnerships could be abolished as the price for getting David Cameron’s plans on to the statute book.

A wrecking amendment tabled by Conservative opponents of same-sex marriage was defeated by 375 to 70 votes after the Tory front bench was supported by the vast majority of Labour and Liberal Democrats.

As the Commons debated the Marriage (Same Sex Couples) Bill, Labour threw Mr Cameron a lifeline in his latest battle with Tory right-wingers. He faced the prospect of losing the vote on the wrecking amendment, which could have delayed the introduction of gay marriage until after the election.

Download the new Independent Premium app Sharing the full story, not just the headlines

A threatened Conservative rebellion faded away with fewer than 50 backbench MPs voting against their leadership line. The outcome – just five days after 116 of his MPs defied Mr Cameron in a Commons vote on Europe – will come as a relief to the Prime Minister.

After a bruising series of clashes with the party grassroots, he wrote to Tory members, insisting he enjoyed a “deep and lasting friendship” with them.

Ahead of the vote, the Government agreed to review the future of civil partnerships as it tried to head off the amendment. The Tory rebels proposed extending civil partnerships to heterosexual couples. Labour and the Liberal Democrats agreed to support the wholesale review as they joined forces with Mr Cameron.

A senior Conservative source said the review would be launched shortly, with a view to completing it by the time of the 2015 general election and would look at all options, including scrapping the ceremonies altogether. The source told The Independent: “How civil partnerships work and whether they continue to exist, the whole thing would be up for grabs.”

More than 53,000 civil partnership ceremonies have been conducted since they became legal in December 2005. People already in such unions would not see them annulled or lose their existing rights, but abolition would mean gay couples would not be able to enter them in future. A decision would depend on the result of a public consultation exercise, but abolition would be politically risky and could run into opposition.

Ben Summerskill, chief executive of the gay equality group Stonewall, said: “There are people who were required to have civil partnerships and want to keep them. If over time, they wither on the vine, so be it. That is unlikely to happen in the lifetime of this parliament.”

With large numbers of Tory MPs opposed to gay marriage, Mr Cameron had to rely on the votes of Labour and Lib Dem MPs to defeat a series of earlier amendments tabled by Tory opponents. They included a move to protect registrars who do not wish to conduct same-sex marriage ceremonies. It was thrown out by 340 to 150 votes, with rebels against the leadership line including Cabinet ministers Iain Duncan Smith and Owen Paterson.

In a heated Commons debate, traditionalists accused their party leadership of ignoring widespread backbench opposition to speed the contentious measure into law. Sir Gerald Howarth, an ex-minister and former aide to Margaret Thatcher, said there was no Conservative majority in favour of gay marriage and said the policy was not contained in any party’s manifesto.

He added: “I fear that the playing field has not been levelled. I believe that the pendulum is now swinging so far the other way and there are plenty in the aggressive homosexual community who see this as but a stepping stone to something even further.”

Senior Tories closed ranks to reject a demand for an inquiry into claims the party’s co-chairman, Lord Feldman, ridiculed activists as “swivel-eyed loons”.

The Conservative Party Board threw out a call to examine the allegations which are strongly denied by Lord Feldman, a close friend of Mr Cameron.

Mr Cameron told activists: “I would never have around me those who sneered or thought otherwise.”