British legislators have approved gay marriage despite fierce opposition from members of Prime Minister David Cameron's Conservative party.
Members of the House of Commons - the lower House - voted on Tuesday by 400 to 175 to approve the draft law allowing same-sex couples to marry in England and Wales.
The move puts Britain on track to join the ten countries that allow same-sex couples to marry, but Cameron had the embarrassment of seeing more than half of his Conservative legislators refusing to back him.
Just 127 of 303 Conservatives voted in favour of the plans, with 136 voting against and 40 more either formally abstaining or not voting.
"Strong views exist on both sides but I believe MPs voting for gay people being able to marry too, is a step forward for our country," Cameron wrote on his Twitter page after the vote.
The government-proposed bill would enable gay couples to get married in both civil and religious ceremonies, provided that the religious institutions consent.
The vote was warmly welcomed by Cameron's junior coalition partners, the Liberal Democrats, and by the opposition Labour party, while gay rights group Stonewall called the result "a truly historic step forward".
Deputy Prime Minister Nick Clegg, the Liberal Democrats leader, called the result a "landmark for equality".
"Tonight's vote shows parliament is very strongly in favour of equal marriage," he said. "Marriage is about love and commitment, and it should no longer be denied to people just because they are gay."
Currently, same-sex couples only have the option of a civil partnership, which offers the same legal rights and protections on issues such as inheritance, pensions, and child maintenance.
During a debate that lasted more than six hours, many Conservative MPs denounced the legislation, saying it was morally wrong, not a public priority, and unnecessarily divisive.
Conservative lawmaker Gerald Howarth told parliament that the government had no mandate to push through a "massive social and cultural change".
Culture Secretary Maria Miller, the minister responsible for the legislation, insisted the bill would protect religious freedoms and "not marginalise those who believe marriage should be between a man and a woman".
The Church of England, the country's official faith, is barred from performing such ceremonies.
That provision aims to ensure that the Church, which opposes gay marriage, is protected from legal claims that as the official state religion it must marry anyone who requests it.
The bill must next be scrutinised by a committee of legislators and then go before the upper chamber the House of Lords before becoming law.
While a majority of people in Britain back gay marriage, polls show that Cameron's strong support for the issue could undermine his party's chances at the next general election in 2015.