The Deputy Prime Minister Nick Clegg has warned Conservative backbenchers that he intends to follow through a policy to allow gay marriage.
The policy has come under threat after the Tories' and the Lib Dems' battering at the local elections earlier this month. The poor results have fuelled speculation that David Cameron may attempt to retreat on some of the coalition's more controversial legal reforms, in a bid to appease angry Tory MPs.
However, speaking out in favour of the policy, Mr Clegg has warned his Conservative coalition partners that it will be a case of "how, not whether" gay marriage will be legalised.
It is thought that the proposal will be put to a free vote in the House of Commons as a matter of conscience.
Owen Paterson, the Conservative Northern Ireland Secretary has become the first minister to oppose the policy in public. In a letter to a constituent Mr Paterson said that after giving the matter careful consideration he has decided that it is not a policy that he can support.
Opposition to the policy is already mounting, with some half a million signatures committed to a petition organised by the Coalition for Marriage group. The group has support from a number of backbench Tory MPs and church leaders.
The group lobbying for the policy is the Coalition for Equal Marriage.
Mr Clegg told them: "The Coalition Government, the Liberal Democrats and I remain wholeheartedly committed to lifting the ban on equal civil marriage. We are currently consulting on how, not whether, to introduce proposals for equal marriage and I want to encourage everyone to make sure that their voices are heard during this time."
Mr Clegg pointed to the fact that gay marriage was already permitted in many of the world's leading democracies. The Netherlands was the first country to introduce a law back in 2001. Since then nine other countries have joined them, including Belgium, Spain and Sweden, South Africa and Canada. Policies to permit same-sex marriage are also under consultation in a further ten countries.
Conor Marron is the co-founder of the Coalition for Equal Marriage, he told the Independent.
"We're very happy to have Nick Clegg standing with us on this issue, along with the majority of MPs who have voiced their position on the subject."