Plans to allow gay marriage look set to overcome their latest parliamentary hurdle after Labour and the Government signalled they were ready to work together to defeat a backbench bid to wreck the legislation in the House of Commons.
A source close to Culture Secretary Maria Miller said she was "very relaxed" about a Labour proposal for an immediate consultation on extending civil partnerships to heterosexual couples, designed to defuse Tory backbench demands for straight couples to be given equality with homosexuals and lesbians in this area.
The deal means that the first same-sex marriages could take place as early as next summer if the Marriage (Same Sex Couples) Bill clears the House of Lords, where it is expected to meet stiff resistance.
A Tory opponent of gay marriage has tabled a "wrecking amendment" to the Bill which would extend the option of civil partnerships to straight couples. While many advocates of same-sex marriage back the idea in principle, they fear it could delay the legislation or scupper it altogether after Mrs Miller said it would impose "significant" additional complexities and extra costs on the reforms.
The wrecking amendment, tabled by former families minister Tim Loughton, is expected to win the support of 100 or more Conservative backbenchers in a free vote in the Commons, but it needs the backing of large numbers of Labour or Liberal Democrat MPs to have any chance of being passed.
Lib Dem leader Nick Clegg has made clear that he would not back amendments that would derail the Bill, and Labour has put forward plans for an immediate consultation on straight civil partnerships, which is expected to be enough to persuade the party's MPs not to back the Loughton amendment.
Downing Street signalled Prime Minister David Cameron's readiness to support the Labour proposal, saying it was "entirely consistent" with an amendment tabled last week by Mrs Miller which would require a future culture secretary to review civil partnerships five years after the introduction of gay marriage - but leaves open the option of an earlier review. It is understood Mrs Miller's amendment was deliberately phrased in a vague way to allow an earlier review if there is pressure from Parliament for it to be conducted swiftly.
Gay marriage is the latest in a series of issues sparking friction between Mr Cameron and traditionalist Tory MPs and activists. A group of more than 30 current and former local party chairmen have written to the PM to warn that it will drive Tory voters to Ukip and make a Conservative election victory in 2015 impossible.
Mr Loughton has denied that his amendment is designed to derail the Bill, insisting that it is a matter of equality that heterosexuals too should be able to have civil partnerships. "If the Government think it is right to extend marriage to everyone then it has to be right to extend civil partnerships to everyone too," he said.
A move to allow registrars who oppose gay marriage to refuse to officiate at same-sex ceremonies was comfortably rejected, despite attracting the support of 150 MPs. In the first of a series of votes on amendments tabled by opponents, the change was rejected by a majority of 190 - 340 MPs voting against it.