The Chancellor, George Osborne, has likened the introduction of gay marriage to William Wilberforce’s campaign to abolish slavery.
The contentious remark, made at the Conservative Party Conference, risks offending black majority churches that disagree with same-sex marriage.
Mr Osborne said gay marriage was a “landmark piece of social legislation”.
He said: “There is a Conservative story which is not told often enough.
“Of William Wilberforce, being the man who freed the slaves, of Shaftesbury, who said we will limit factory hours and we are not going to let children work down the mines.
“That is a very powerful part of the Conservative story and it is a part that I am very happy to associate myself with.”
He admitted that redefining marriage was probably not “universally popular” with the members of his audience.
Earlier this year, John Glen MP hit out at comments comparing support for traditional marriage with support for slavery or apartheid.
He said the remarks were “deeply unhelpful” and “particularly offensive to those in black majority churches” who oppose the redefinition of marriage.