Conservative MPs have spoken out against prime minister David Cameron’s support for gay marriage.

On Wednesday, Mr Cameron urged the party to back the move because of its Conservatism, not in spite of it.

Gerald Howarth, a junior defence minister, told The Daily Telegraph that gay unions could not be considered marriage.

He said: “Some of my best friends are in civil partnerships, which is fine, but I think it would be a step too far to suggest that this is marriage. I take the view that marriage can only be between a man and a woman. That is what Christian marriage is about.”

The Tory MP for Wellingborough, Peter Bone, said the prime minister’s remarks were “political correctness”.

Catholic Church leaders have also challenged Mr Cameron’s support for the issue.

The Most Rev Peter Smith, the Archbishop of Southwark, welcomed the support for marriage but accused the prime minister of trying to “redefine” the institution.

The Catholic Bishop of Arundel and Brighton, the Rt Rev Kieran Conry, said the church would “have to do something” to protect marriage.

A government consultation on “how” to legalise gay marriage will begin in spring 2012.