Catholic bishops say the church opposes any "redefinition" of marriage, The Daily Telegraph reported. A spokesman said the Church of England continues to believe marriage is between a man and woman.
Cameron, in his keynote speech to the Conservative Party conference, said Wednesday gay marriage is about "commitment" as well as equal rights.
"Conservatives believe in the ties that bind us; that society is stronger when we make vows to each other and support each other," he said. "So I don't support gay marriage despite being a Conservative. I support gay marriage because I'm a Conservative."
Peter Bone, a Conservative backbencher, told the Telegraph Cameron's position is "political correctness." Gerald Howarth, a junior defense minister, said Conservative legislators should be given the option of opposing same-sex marriage if it comes to a vote.
Southwark Archbishop Peter Smith, one of the country's leading Catholic clerics, said the state must not redefine marriage.
"Whilst we welcome the Prime Minister's support of marriage, family life and especially the care of children, the proposed redefinition of marriage cannot be right," he said.
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