Liberal Democrat minister Vince Cable has said that changing the definition of marriage is unnecessary.
Dr Cable, who is the Secretary of State for Business, said that he thought the “status quo is fine” with civil partnerships.
However he also said if the issue came to a vote, he would back the Government.
Dr Cable, in a letter to a constituent, said: “On the issue of same-sex marriage, my own personal view is that the status quo is fine, with same-sex couples being able to commit in a civil partnership.”
But he added “if it comes to a vote I would vote in favour of same-sex civil marriage”.
In May it was revealed that Lib Dem leader Nick Clegg will force his MPs to vote for redefining marriage. However Conservative MPs – including ministers – will get a free vote on the issue.
Responding to Vince Cable’s comments, Colin Hart, of the Coalition for Marriage, said: “This astonishing letter reveals yet more splits in the Government and highlights why Nick Clegg is wrong to say he will whip his MPs through the lobby.
“Dr Cable is clearly expressing the sense of unease amongst the Liberal Democrats, who like their coalition partners and the Civil Service, are starting to realise that rewriting the traditional definition of marriage is extremely difficult and is likely to have serious repercussions on ordinary people, schools, institutions like churches and charities that oppose the change.”
Earlier this month secret Government emails revealed that schools could be forced to teach children about gay marriage if it becomes law.
The emails between officials at the Home Office and Department for Education came to light following a Freedom of Information request.
One official said the issue was a potential “minefield” and wanted “defensive lines to take” in case the press started asking questions.