Voting on gay marriage is not "an imposition on religion or churches" and should not be left to MPs' consciences, Nick Clegg said on Sunday.

The Deputy Prime Minister and Liberal Democrat leader said his MPs would back legislation legalising same-sex marriages - unlike some of their coalition partners.

Tory MPs will be allowed to vote either for or against same sex marriage, to avoid a rebellion from Tory MPs and ministers opposed to the issue.

Mr Clegg differentiated himself from his coalition partner saying it was up to Prime Minister David Cameron whether he forced Conservative MPs to support the measure, but vowed Lib Dems would "honour what we have said as a party".

"We are not asking any person with religious convictions to sacrifice anything.

"We are simply saying those who want to show a lifelong commitment to each other should be able to do so."

Commons Leader Sir George Young last week confirmed MPs would be offered a free vote, saying: "Along with other issues 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 and that is what we plan to do."

But Mr Clegg told BBC1's Andrew Marr Show: "In the same way the civil partnerships legislation which was introduced under Labour was a whipped vote, I personally don't think this is something which should be subject to a great free for all because we are not asking people to make a decision of conscience."

He added: "If this was an issue that somehow the government was proposing something that would somehow be an imposition on religion or the churches, then of course that would be a matter of conscience. We are not."

Critics have questioned Mr Cameron's commitment to the reform after he conceded to a free vote to quash an expected a rebellion among backbench Tories.

Conservative Cabinet minister Northern Ireland Secretary Owen Paterson also declared his opposition to same-sex marriage in the most high-level challenge to Mr Cameron so far on the issue, while defence minister Gerald Howarth is also against the move.

Tory critics view the proposal as a Liberal Democrat policy distracting the government from bigger challenges.

Meanwhile Sinitta is the latest celebrity to back a campaign supporting global equal marriage rights for gay couples, Out4Marriage.

The singer said: "I believe in love and I also believe in marriage. I've been married and I hope one day to marry again.

"Most of all I believe in all people being able to celebrate their love in marriage; gay people, straight people, black people, white people - all people. That's why I'm Out4Marriage, are you?"

Sinitta joins entrepreneur Sir Richard Branson, girl group The Saturdays, comedian David Walliams, shadow home secretary Yvette Cooper, actor and writer Stephen Fry and gay rights campaigner Peter Tatchell, who have all given their support to the campaign

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