Image caption A number of his ministers have publicly opposed gay marriage

Downing Street has denied back-tracking on gay marriage after it was revealed Tory MPs - including ministers - will be allowed a free vote.

On Wednesday, David Cameron's spokesman said legislating on the issue was a "a government commitment" and ministers would be expected to support it.

On Thursday, No 10 said they saw it as an issue of conscience, like abortion, and it was right to allow a free vote.

Sources said they were still confident of getting the measure through.

The prime minister has personally backed the plan to allow same sex couples in England and Wales to marry, which is currently the subject of a consultation.

On Thursday morning, Mr Cameron's official spokesman said the PM had not changed his mind and the government was committed to introducing same sex civil marriage by the end of the current Parliament.

'Perfectly proper'

But the spokesman stressed the consultation was "still ongoing" and refused to speculate on whether cabinet ministers would be expected to vote for it, adding that there were "free votes in the House of Commons from time to time".

Commons leader Sir George Young told MPs: "Along with other isssues that involve matters of conscience, it seems to me perfectly proper that this should be subject to a free vote on this side of the House."

The plan is expected to be backed by many MPs from all three of the largest parties - but some leading Tories have called for it to be dropped, in the wake of bad local election results, arguing there are more pressing priorities for voters.

Current legislation allows same-sex couples to enter into a civil partnership, but not civil marriage.

A free vote means that MPs are allowed to vote as they wish and not as directed by party managers.

In a letter to a constituent published on the Politicshome website , Northern Ireland Secretary Owen Paterson said: "Having considered this matter carefully, I am afraid that I have come to the decision not to support gay marriage."

Children's Minister Tim Loughton has also expressed doubts about the plan, writing on his website : "I have to say that my instinct is not to support these proposals and, as it stands, I intend to vote against measures to legalise gay marriage."

Defence Secretary Philip Hammond has said that gay marriage is not a priority and the government has to focus "on the things that matter to the people in this country".

At the Conservative Party conference in 2011, Mr Cameron told delegates: "Conservatives believe in the ties that bind us; that society is stronger when we make vows to each other and support each other.

"So I don't support gay marriage despite being a Conservative. I support gay marriage because I'm a Conservative."