Anglicans have joined with the Catholic church in opposing new laws that would force faith-based adoption agencies to allow gay couples to adopt children.
Archbishop of Canterbury Rowan Williams and the archbishop of York, John Sentamu, have written to Tony Blair warning that "the rights of conscience cannot be made subject to legislation, however well meaning".
Their intervention comes after the head of the Catholic church in England and Wales, Cardinal Cormac Murphy O'Connor, warned many Catholic adoption agencies would rather close than comply with new sexual orientation regulations.
Yesterday Downing Street said the prime minister was considering the interventions, arguing it was "not a straightforward black and white issue, this is an issue in which there are sensitivities on all sides and they have to be respected".
He has one eye on crucial elections in Scotland later this year, and the ongoing row threatens to alienate many of the 800,000 Catholics north of the border.
However, reports suggest the majority of the cabinet would revolt if the regulations, which were introduced in Northern Ireland on January 1st and should be enforced in England and Wales this spring, are modified.
Labour MP Chris Bryant last night defended the regulations, which make it illegal to refuse goods or services to people on the grounds of their sexual orientation, saying: "We should not countenance prejudice in the public sphere."
He told Channel Four News: "You shouldn't have hotels, restaurants and hospitals being able to say 'no gays', just as they are not able to say 'no blacks' or, for that matter, 'no Catholics'."
Another Labour MP, Angela Eagle, told BBC Two's Newsnight: "The point here is that in the matter of anti-discrimination laws and protection we cannot have exemptions.
"We cannot say that somebody is protected on the grounds of their sexual orientation if, in fact, bits of the system giving public services can say they can exempt themselves."
In their letter today, the two archbishops warn that the debate threatens to "polarise opinions", particularly in the assertions that the minister in charge of driving through the laws, devout Catholic Ruth Kelly, is privately opposed to the proposals.
But they say: "Many in the voluntary sector are dedicated to public service because of the dictates of their conscience.
"In legislating to protect and promote the rights of particular groups the government is faced with the delicate but important challenge of not thereby creating the conditions within which others feel their rights to have been ignored or sacrificed, or in which the dictates of personal conscience are put at risk."
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