MPs' debate is expected to be formality after House of Lords passed same-sex marriage bill on Monday
Legislation to introduce same-sex marriage is expected to complete its passage through the House of Commons on Tuesday, with the first weddings under the law to take place in England and Wales next summer.
Jubilant gay rights campaigners were celebrating the successful passage of the marriage (same-sex couples) bill through the House of Lords on Monday night – and vowing to take the fight for marriage equality to Scotland and Northern Ireland.
MPs will debate amendments made to the legislation in the upper house on Tuesday evening, but this is expected to be little more than a formality and is unlikely to delay its progress into law, with royal assent within the next few days.
The deputy prime minister, Nick Clegg, told campaigners celebrating outside parliament that the new law would ensure that lesbian, gay, bisexual and transgender (LGBT) people felt "recognised and valued, not excluded".
And the gay Labour peer Lord Alli told fellow members of the second chamber – some of them sporting pink carnations: "My life and many others will be better today than it was yesterday."
But opponents of gay marriage warned that the government-backed reform would "come back to bite" the prime minister, David Cameron. The Coalition for Marriage campaign group said it would mobilise its support base in next year's European elections and the general election of 2015.
The coalition chairman, Colin Hart, said: "Mr Cameron needs to remember that the Coalition for Marriage has nearly 700,000 supporters, nearly six times the number of members of the Conservative party. They are just ordinary men and women, not part of the ruling elite. They are passionate, motivated and determined to fight on against a law that renders terms like husband and wife meaningless and threatens one of the foundations of the institution of marriage: fidelity and faithfulness."
The bill survived a stormy passage through the Commons despite fierce opposition from dozens of Tory backbenchers, and then overcame an attempt to "wreck" it in the House of Lords last month.
James-J Walsh, campaigns director of Out4Marriage, hailed the Lords' approval of the bill as "a momentous occasion in lesbian and gay equality in England and Wales, overcoming the last major hurdle on our path to full legislative equality".
Walsh added: "With this legislation Britain shines a light as one of the most progressive countries in the world, and manages to balance both lesbian and gay rights with religious freedoms."
The Stonewall chief executive, Ben Summerskill, said: "It is impossible to express how much joy this historic step will bring to tens of thousands of gay people and their families and friends. The bill's progress through parliament shows that, at last, the majority of politicians in both houses understand the public's support for equality – though it's also reminded us that gay people still have powerful opponents."
The Equal Love campaign co-ordinator Peter Tatchell said: "This vote is a defeat for discrimination and a victory for love and marriage. After a 21-year-long campaign, we are now on the cusp of same-sex marriage but not quite marriage equality."
Clegg said the bill was a mark of "the kind of open, modern, tolerant and diverse society we want Britain to be in the 21st century".
Writing on the PinkNews website, the Liberal Democrat leader said: "Civil partnerships were a landmark reform. And not every couple, gay or straight, feels that they need to get married to affirm their commitment to each other.
"But only the right to marry, if that's what you so choose, is true equality. It lets every member – young or old – of our LGBT community know that they are recognised and valued, not excluded. It finally ensures that all loving couples have the freedom and right to make that commitment to each other in our society."
The Labour leader, Ed Miliband, told PinkNews: "The last Labour government was responsible for landmark changes in the law such as repealing section 28, equalising the age of consent and introducing civil partnerships. I am proud that equal marriage, a hugely important step forward in the fight for equality in Britain, is one which was achieved with the support of the whole of Labour's shadow cabinet and the vast majority of Labour MPs and peers."
Paul Parker, recording clerk for Quakers in Britain, said that Tuesday's development "brings us tantalisingly close to legal recognition for same-sex marriages in our Quaker meetings".
Along with the Unitarians and Free Christians and Liberal and Reformed Judaism, Quakers have made clear their intention to stage same-sex marriages once the law is changed.
Parker said: "We relish the freedom to express our faith by treating all our committed couples in the same way. The voice of minority faith groups has been heard on this. We respect others who do not yet share our view. For Quakers, this is a matter of religious freedom."