Churches will be allowed to conduct same-sex marriages in the UK it was revealed over the weekend.

The move 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 Daily Telegraph reports.

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.

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 one hundred per cent 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.”

However, opponents of the proposed legislation 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: “The Government is not seeking to change how religious organisations define religious marriage and 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 they were first introduced by Tony Blair they were to be conducted solely by civil registrars.

But the Coalition 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.

“What is even more alarming is the PM has gone back on his promises that Churches will be protected. The suggestion that by creating an ‘opt in system’ you somehow prevent churches, mosques and synagogues being sued is risible. This is now made much more likely.

“Any legislation that the PM proposes will be subject to the European Courts, who according to legal experts will find against the Government and those religious institutions who end up in the dock.

“So the PM is writing a cheque that he knows will bounce.”

In June, the former Archbishop of Canterbury, Dr George Carey, warned that Government promises to protect Churches from lawsuits attempting to force them to carry out same-sex marriage could not “last the test of time”.

Writing in the Daily Telegraph, he said: “Religious bodies will eventually be permitted to conduct same-sex marriage, and how long can it be before a civil right to equal marriage is forced on every denomination?

“In Denmark, under new laws, the state church has to permit same-sex marriage in all its buildings. Clergy can continue to refuse, but their bishops have to find another celebrant.”

“Unintended consequences cannot be known for sure, but can be reasonably charted in the light of recent experience. For example, who could have predicted when human rights legislation was enacted that regulations would one day drive Roman Catholic adoption agencies out of business? Did legislators ever envisage that their efforts to preserve diversity would lead to Christians being barred from wearing crosses at work?”

Meanwhile, the Catholic bishop of Motherwell in Scotland, James Devine has accused the Prime Minister of being “devoid of moral competence”.

In a two page letter to Mr Cameron, he said that that no one believed his Government’s promises that the Churches will be immune from legal action by gay activists if same-sex marriage was legalised.

The bishop also attacked the Prime Minister over his government’s pursuit of a legal case at the European Court of Human Rights against Christians being allowed to wear crosses at work. Such contradictions between Cameron’s words and actions, Bishop Devine wrote, “only serve to compound our perplexity about the imperfect fit between your statements and actions. You appear to be creating a political culture in which words mean nothing.”

“You vacillate, ambivalent about the role you wish to perform – the disciple of David or Nero,” the bishop wrote. “With such a contradiction between your statements and actions, on what basis can you expect anyone – Christians in particular – to trust or respect you?”