David Cameron faces a renewed backlash from Tory MPs over gay marriage after attempted reassurances over church rights failed to quell backbench anger.
Culture Secretary Maria Miller promised a "quadruple lock" to prevent religious institutions being forced to marry same-sex couples against their will. But it did little or nothing to assuage anger amongst many party colleagues bitterly opposed to the reform however, or to ease opposition from church leaders.
A move to exempt the Church of England and the Church in Wales from the new rules also drew criticism from gay rights groups leading the pro-marriage campaign.
Mrs Miller was confronted by a succession of hostile Tory MPs when she set out the Government's plans to extend marriage rights to same-sex couples by 2015 in the Commons on Tuesday.
Churches which wish to opt in to the system - such as the Quakers - will be able to but specific legal measures will be included to ensure others can retain a ban.
In a sign of the depth of feeling, senior Tory backbencher Brian Binley afterwards published an open letter to the Prime Minister warning "countless" activists were abandoning the party. "It is not just the standing of the leadership which is imperilled through this approach, but our entire political credibility," he said.
UK Independence Party leader Nigel Farage added to the pressure on the Tory leadership by vowing to exploit the controversy to snatch the votes of disaffected Conservatives. Mr Farage told the Guardian the proposal could "rip apart the traditional rural Tory vote" and would be "an affront to millions of people in this country for whom this will be the final straw".
Labour and the Liberal Democrats confirmed they would match the free vote being given to Tory MPs but both party leaders said they were confident of overwhelming support. Ed Miliband said it would be the votes of a unanimous shadow cabinet and the "vast majority" of backbenchers that would get the measure passed by the Commons, but he said he was disappointed by the proposal to ban gay marriages in the two churches.
The move also dampened the celebrations of gay rights groups. Out4Marriage campaign director James-J Walsh said the Government had forged "a real feeling of hope" on the issue by pressing ahead with the reforms. But he warned the package could be undermined by the so-called "fourth lock" which could leave worshippers legally barred from marriage even if the institution dropped its own opposition.
Some religious leaders maintained their vehement opposition to same-sex marriage and complained that a public consultation over the plans had been a "shambles". The Anglican Bishop of Leicester, the Rt Rev Tim Stephens, warned of a "troubling" division between the political class and the vast majority of practising religious people.