Cardinal Keith O’Brien said the new sexual orientation regulations in the Equality Act were a “threat to religious freedom”.

The changes, due to be introduced next year, will make it illegal for businesses or public bodies to discriminate against gay people in the provision of goods, facilities or services.

They will outlaw sexual orientation discrimination in the classroom by forcing schools to give lessons about homosexuality and heterosexuality equal prominence.

The Catholic church in Scotland is demanding an exemption that would allow it to conduct sex and relationship classes in line with its beliefs and deny homosexuals the use of its premises, such as church halls.

The move threatens to reignite the bitter row that surrounded the repeal of section 28, the law that banned the promotion of homosexuality in schools.

O’Brien said the new legislation, which is being drawn up by the Department for Communities and Local Government at Westminster, would “force people of faith to approve and co-operate with values that they can never in conscience accept”.

He said: “The role of the state is over-reached when it tramples legitimate moral freedoms and when it imposes values which are without rational and sociological merit.

“Democracy that separates itself from truth, taking the path of moral relativism, can soon become thinly veiled totalitarianism where power is exercised by the strong against the weak.”

Peter Kearney, spokesman for the Catholic church in Scotland, added: “Homosexuality is immoral and it’s not something we would endorse or support.

“We are virtually getting into the realms of a thought crime just because we want to adhere to our religious beliefs. It is telling people what they can and can’t think.”

The planned legislation has also provoked a backlash from religious groups in England, including the Association of Christian Teachers and the Archbishops’ Council of the Church of England.

In addition, the church claims that it threatens the future of Scotland’s two Catholic adoption agencies in Edinburgh and Glasgow.

Last month The Sunday Times revealed that the church-run agencies would be given the right to refuse to hand over children to homosexual couples as part of a compromise written into the adoption bill, which is going through the Scottish parliament. The bill will give unmarried couples, including same-sex couples, the right to adopt.

However, it has now emerged that the bill will be superseded by the sexual orientation regulations, making it illegal for them to turn down prospective adoptive parents on the grounds of their sexuality.

Kearney warned that the church-run adoption agencies could be forced to close.

“What happens if this goes through and a same-sex couple present themselves saying they want to adopt?” he asked.

“We have been told by executive officials that if the legislation goes ahead as expected then the Catholic agencies will not be able to opt out and will have to treat the homosexual couple the same as the heterosexual couple.”

Tim Hopkins, of the Equality Network, a gay campaign group, denied that the legislation threatened religious freedom and insisted that religious groups should not be allowed to opt out.

“In no way is this a threat to religious freedom, there is nothing in the legislation that says the Catholic church must provide mass to a gay person or marry a same-sex couple or stop preaching that homosexuality is a sin.

“However, when an organisation, faith or otherwise is providing a public service, such as education or adoption, it should be bound by the same rules that bind the public and private sector.”

A spokesman for the Department for Communities and Local Government said: “The question of how religious organisations should be covered by the sexual orientation regulations is clearly one of the most sensitive questions ministers are considering.

“The very strong response to the consultation is still being considered and ministers have yet to make any decisions in this area.”

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