Plans to allow same-sex marriage survived a Conservative backlash after a fraught debate in the House of Commons.
An amendment which supporters warned could derail the legislation altogether was easily defeated after the Government reached an agreement with Labour.
The Marriage (Same Sex Couples) Bill now looks set to be approved by MPs tomorrow - but is likely to meet stiff resistance in the House of Lords.
A bid by a Tory opponent of gay marriage to extend civil partnerships to heterosexual couples attracted 70 supporters in a free vote - far fewer than the 100-plus anticipated by some critics.
Ex-minister Tim Loughton insisted it was not a "wrecking amendment" and was a move backed by the public and many advocates of same-sex marriage.But the change - which Culture Secretary Maria Miller said would impose significant delays and costs - was defeated by a majority of 305.