British politicians have backed legalising gay marriage in the first of several votes on the issue.

The draft law, which proposes legalising same-sex marriage in 2014, was carried by 400 votes to 175 votes in the House of Commons.

The vote in the House of Commons was "free", meaning MPs from across the political spectrum were able to vote according to their conscience rather than under party orders.

The legislation is several stages away from becoming law, but debate on the issue has already split Prime Minister David Cameron's ruling Conservative party in two.

In a sign of how divisive the issue has become for Mr Cameron, the finance minister, the foreign secretary and the interior minister wrote a joint letter to a national newspaper today, urging fellow Conservatives to vote in favour.

The new law proposes legalising same-sex marriage in England and Wales in 2014.

It would also allow civil partners to convert their partnerships into marriages.

Gay marriage supporters say while existing civil partnerships for same-sex couples afford the same legal rights as marriage, the distinction implies they are inferior.

A YouGov poll for the Sunday Times on Sunday showed 55% favoured legalising gay marriage, while 36% opposed it.

However, the same poll showed the issue was not one that concerned most voters, placing only 12th in a list of their top 15 priorities ahead of the next election.