David Cameron backed Welsh Secretary David Jones despite the cabinet minister being accused of being "hugely offensive" after he appeared to suggest gay couples could not provide a safe home for children.
Downing Street pointed out that gay marriage was "free vote issue" after Jones said on ITV's Face to Face he regarded marriage "as an institution that has developed over many centuries, essentially for the provision of a warm and safe environment for the upbringing of children, which is clearly something that two same-sex partners can’t do."
Asked whether Mr Cameron found the comments acceptable, a Downing Street source said: "Gay marriage and gay adoption are both conscience issues and, as such, have been treated as free votes.
"The Prime Minister is a supporter of both."
Labour's shadow equalities minister Kate Green branded Jones' remarks "hugely insulting, offensive and wrong".
Andrew White, the director of Stonewall Cymru, said: "We’re saddened that the secretary of state for Wales should make such an offensive and inaccurate remark."
"There are many different types of family in Wales today, including many same sex couples raising children. It’s deeply undermining to families and children when they hear this sort of ill-informed comment."
Jones was one of two Tory cabinet ministers, along with environment secretary Owen Paterson, to vote against David Cameron's plan to introduce same-sex marriages last week.
The Clwyd West MP told ITV that his opposition to gay marriage did not mean he was "in any way opposed to stable and committed same-sex partnerships" and rejected the suggestion of homophobia.
"I've got a lot of people in my life who are very important to me who are gay, anyone who knows me would never accuse me of that [homophobia]," he said.
Responding to the criticism Jones said in a statement: "I was asked on the Face to Face programme why I voted against the same sex marriage proposals. I replied that I had done so on the basis that I took the view that marriage is an institution that has developed over the centuries so as to provide a safe and warm environment for the upbringing of children.
"I made the point of stressing that I was fully supportive of committed same sex relationships. I also strongly approve of civil partnerships.
"I did not say in the interview that same sex partners should not adopt children and that is not my view.
"I simply sought to point out that, since same sex partners could not biologically procreate children, the institution of marriage was one that, in my opinion, should be reserved to opposite sex partners."