David Cameron has just confirmed [2] the report in today's Evening Standard [3] that he will allow religious groups to host gay marriages. He said:

I'm a massive supporter of marriage and I don't want gay people to be excluded from a great institution.

But let me be absolutely 100% clear, if there is any church or any synagogue or any mosque that doesn't want to have a gay marriage it will not, absolutely must not, be forced to hold it.

That is absolutely clear in the legislation.

Also let me make clear, this is a free vote for Members of Parliament but personally I will be supporting it.

The move brings Cameron into line with Nick Clegg and Ed Miliband, both of whom have argued that those groups who are willing to conduct same-sex weddings, such as Quakers and Reform Jews, should be free to do so.

After being warned that a blanket ban would be open to legal challenge, ministers maintain that those religious organisations that oppose gay marriage, including the Church of England and the Roman Catholic Church, will not be forced to host ceremonies. But some Tory MPs argue otherwise. Soon after the Standard's story appeared, Conservative MP Mark Pritchard tweeted [4]: "Exemptions for places of worship in the same-sex marriage Bill likely to be ruled unlawful by the Supreme Court or the ECHR within months". He added that the introduction of gay marriage would "undo much of the good outreach work the Party has done with Muslim, Sikh, and Hindu communities". Also swift to denounce Cameron was Tory MP Stewart Jackson, who declared [5]: "Gay marriage bill will be massacred in the Lords and govt can't use Parliament Act as it wasn't in manifesto. Arrogant Cameron knows best."

But despite the opposition of as many as 118 Tory MPs [6] and a near-majority of Conservative voters, it now seems certain that a free vote on the issue will be held early next year. The government believes that its support for gay marriage puts it on the right side of history and demonstrates its liberal credentials. As George Osborne wrote in the Times [7](£) last month, "Successful political parties reflect the modern societies they aspire to lead".

With the support of the majority of Labour and Lib Dem MPs, the bill will easily make it through the Commons. But Cameron faces one of the biggest battles he has ever fought with his party.