Leading article: MPs must move with the times on gay marriage

David Cameron's decision to allow his MPs to vote freely on the issue of gay marriage is a reasonable one. After all, the matter is indeed one "of conscience". But Home Secretary Theresa May's enthusiastic support – not least her video for the Out4Marriage campaign – blazes a trail that her Conservative colleagues should follow.

Since the decriminalisation of homosexuality less than 50 years ago, public opinion has changed at immense speed. Neither is it credible to continue stoutly to insist that society benefits from stable family relationships, while refusing to recognise those between people who are gay. And the "separate but equal" argument fails now just as it did when used to support racial discrimination.

Civil partnerships were a step forward; through them, gay marriage is effectively a reality. But the final barrier to equality must now be lifted. MPs, even Tory ones, must move with the times.