British lawmakers voted in favour of controversial legislation allowing gay marriage on Tuesday despite fierce opposition from members of Prime Minister David Cameron's own party.
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 half of his Conservative legislators refusing to back him.
The prime minister insists that the plan to allow same-sex couples to marry in England and Wales would "make our society stronger" although the draft law still has several other parliamentary hurdles to clear.
It passed by 400 votes to 175, mainly because it had overwhelming support from the opposition Labour Party and also from many members of the Liberal Democrat party, the junior partner in Cameron's coalition government.
British media said around 140 Conservatives voted against and around 130 in favour with some 40 abstentions.
Cameron had allowed lawmakers a free vote on the issue, meaning they were not directed by party managers.
Speaking before the vote, Cameron said: "Today is an important day. I am a strong believer in marriage, it helps people commit to each other, and I think it is right that gay people should be able to get married too.
"This is, yes, about equality. But it is also about making our society stronger.
"I know there are strong views on both sides of the argument — I accept that. But I think this is an important step forward for our country."
Opponents attacked the bill during an often impassioned day-long debate ahead of the vote in the House of Commons, or lower house of parliament.
Pleas from Cameron's heavyweight cabinet allies to persuade their Conservative colleagues to back his plans and avoid damaging divisions fell on deaf ears.
A former junior defence minister, Gerald Howarth, said the government had no mandate for such a "massive social and cultural change".
"I believe this bill is wrong, the consultation was a complete sham. It has caused deep and needless divisions within the Conservative Party," he said.
Another Conservative opponent, Roger Gale, said the legislation was "Orwellian".
"Marriage is the union between a man and a woman, has been historically, remains so. It is Alice in Wonderland territory, Orwellian almost, for any government of any political persuasion to seek to come along and try to re-write the lexicon," he said.
Same-sex couples in Britain have had the right to live in civil partnerships since 2005 but cannot marry.
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 push to win over those Conservatives still bitterly opposed to gay marriage was led by three senior party members — finance minister George Osborne, foreign minister William Hague and interior minister Theresa May.
In a letter to the Daily Telegraph, they said "attitudes to gay people have changed" and same-sex marriage was "the right thing to do at the right time".
The proposals are opposed by the Church of England and its new Archbishop of Canterbury Justin Welby, but the legislation bans the "official" churches from offering gay marriage.
The bill must next be scrutinised by a committee of lawmakers 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.
The issue has not however sparked the impassioned protests seen in France, where the National Assembly on Saturday overwhelmingly approved a key piece of legislation that will allow homosexual couples to marry and adopt children.