GAY couples would be allowed to marry in churches under plans due to be unveiled.
The decision by the British Government represents a major U-turn on the position set out in a formal government consultation earlier this year, which proposed a blanket ban.
It raises the prospect of a major battle between church and state over the issue, as well as a massive backbench rebellion, with at least 130 Conservatives set to vote against the proposals.
The plans will be announced by the Culture Secretary Maria Miller next week and a detailed bill is expected to be put before parliament next month.
That could see the redefinition of marriage sped through the Commons before the summer.
The shift in policy came after government lawyers came up with plans for "multiple lock" legal protections for churches, mosques and synagogues which do not want to marry gay couples on grounds of belief.
Prime Minister David Cameron 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 100pc 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."
Opponents believe that no safeguard will be able to protect them from a legal challenge at the European Court of Human Rights, which would force them to marry gay couples.
The official consultation document published in March said: "Any subsequent legislation would be clear that no religious organisation could conduct a religious marriage ceremony on religious premises for same-sex couples."
But now the proposals are expected to be modelled on arrangements already in place for civil partnerships. When these were first introduced by Tony Blair, they were to be conducted solely by civil registrars.
But the coalition government recently changed the law to allow those religious groups which want to conduct civil partnership ceremonies to do so.
It means that the Church of England could only ever perform civil partnerships if the General Synod gives its approval.
But other churches, including the Unitarians, have already begun carrying them out, with their own ministers acting as civil registrars.
But opponents condemned the U-turn as a broken promise.
Colin Hart, Campaign Director for the Coalition for Marriage, said: "The decision to press ahead with the profoundly undemocratic proposals to rewrite the traditional meaning of marriage is deeply disappointing and regrettable."
However, Benjamin Cohen, of Out4Marriage campaign said: "We're delighted to hear that the Government will be legislating to introduce full equal marriage, including same-sex marriages solemnised by religious ministers." (©Daily Telegraph London)