The Most Rev. Vincent Nichols, archbishop of Westminster, said he would tell same-sex Catholic couples who ask about marriage that "what they are called to is not marriage but a very profound and lifelong friendship," The Daily Telegraph reported Friday.
"I would want to say to them that I understand their desires; that I understand their experience of love is vitally important in their lives, but I would want to say to them that they are called in my view, in the church's view, to a very profound friendship in life," Nichols said.
On Thursday, Home Office Secretary Theresa May and Equalities Minister Lynne Featherstone released a consultation paper that would allow same-sex couples to register civil marriages.
Nichols said he found it "utterly astonishing" the consultation didn't include a reference to children.
"It is excluding things that are of the very nature of marriage," he said. "What society says, I believe, is the best circumstances for conceiving and bringing up children is the partnership between two natural parents. That's why the law is there to protect marriage, and that's why the change in the definition of marriage affects everybody."
Nick Herbert, the Home Office shadow minister, said the archbishop has a "sad misunderstanding" of the nature of homosexual relationships.
"It is akin to a union between a man and a woman in a heterosexual marriage," he said. "What is wrong with wanting to show a commitment towards someone?"