One of the UK’s top Catholic bishops has warned Prime Minister David Cameron (pictured) not to redefine marriage.

The Most Rev Peter Smith, the Archbishop of Southwark was responding to Mr Cameron’s speech to his party conference earlier this week in which he said he supported plans to legalise gay marriage.

The Prime Minister said “commitment” in relationships should be valued regardless of whether it involved “a man and a woman, a woman and a woman, or a man and another man”.

However, Archbishop Smith said that while the Catholic Church welcomed the Prime Minister’s support of marriage and family life “the proposed redefinition of marriage cannot be right”.

“Marriage by its very nature is between a man and a woman and it is the essential foundation of family life. The state should uphold this common understanding of marriage rather than attempting to change its meaning.”

According to a report in the Daily Telegraph, the Catholic Church in England and Wales and the Church of England are likely to lodge formal objections to the move when the Coalition launches an official consultation next year.

Speaking to the Conservative Party Conference in Manchester, Mr Cameron said: “We’re consulting on legalising gay marriage. To anyone who has reservations, I say: Yes, it’s about equality, but it’s also about something else: commitment.

“Conservatives believe in the ties that bind us; that society is stronger when we make vows to each other and support each other.

“So I don’t support gay marriage despite being a Conservative. I support gay marriage because I’m a Conservative.”

Under Coalition reforms, churches, synagogues and other faith centres will be able to host same-sex civil partnership registration ceremonies for the first time, including the use of religious music.

Ministers will begin a separate consultation on whether to redefine civil “marriage” to include same-sex couples in the spring.

The Prime Minister was immediately criticised by Christian leaders.

The Catholic Bishop of Arundel and Brighton, the Rt Rev Kieran Conry, warned that Mr Cameron would not be given “an easy ride on this”.

“I think the Church will have to do something. We can’t just let this slide by and say we are not interested,” he said.

“It is the question of protecting the particular, specific institution of marriage and its specific character as the permanent union of a man and a woman who would then bring up their own children.”

Bishop Conry questioned the need to allow homosexual couples to use the term “marriage”.

The Church of England is also likely to oppose the reforms. In response to the Prime Minister’s speech, a spokesman for the Church of England said: “The Church’s view remains of marriage as the life-long union between a man and a woman.”

Andrea Williams, director of Christian Concern, said Prime Minister’s attempt to redefine marriage would have “catastrophic consequences” for society. “The complementary union of a man and a woman in marriage is where love, life, stability and the full flourishing of society begins. He ignores this fundamental principle at his peril.”

Dr Dave Landrum, director of advocacy at the Evangelical Alliance said: “In seeking to re-define marriage David Cameron may have kept the coalition happy, but may also have signalled the end of conservatism. If you can’t conserve the institution of marriage, what can you conserve?”

The gay rights group Stonewall and other campaigners for homosexual equality welcomed Mr Cameron’s words. Chris Bryant, the Labour MP, who is in a civil partnership, said on Twitter: “I hear Cameron backed gay marriage. If so I warmly applaud him.”