The Catholic Church was yesterday accused of attempting to blackmail the government after warning its adoption agencies could close in the face of new gay rights legislation.

Two Scottish Catholic adoption agencies - St Andrew's Children's Society in Edinburgh, and St Margaret's Children and Family Care Society in Glasgow - are among those which could close if new legislation forcing them to accept adoption by gay couples is introduced.

Roman Catholic bishops in Scotland yesterday added their voice to calls for Prime Minister Tony Blair to exempt Catholic adoption agencies from being compelled to place children with same-sex couples.

Mario Conti, the Archbishop of Glasgow, sent a letter to the Prime Minister by fax on behalf of Scotland's Catholic bishops. He will also write to Scottish First Minister Jack McConnell asking him to uphold assurances which he said were given to the Church by the Scottish Executive that they would not expect Catholic agencies to act contrary to their beliefs.

The archbishop's action came as secular and gay rights activists accused Cardinal Cormac Murphy-O'Connor, the leader of the Catholic Church in England and Wales, of using "blackmail" in a bid to secure exemptions from the government.

The cardinal has urged ministers to avoid the "unnecessary tragedy" of the Church's adoption services closing. He wrote to cabinet ministers saying Church teaching prevented its agencies placing children with homosexuals.

Last night he said: "I'm not blackmailing anybody. I am just saying to the government the possible consequences of carrying through those particular regulations."

In his letter, Archbishop Conti, who is vice president of the Bishops' Conference, wrote: "The Catholic Bishops of Scotland express their support for the position taken by Cardinal Murphy-O'Connor."

The row is said to have split the cabinet. Communities Secretary Ruth Kelly, who is Catholic, is reported to be pushing for an exemption.

Peter Tatchell, of the gay human rights group OutRage, claimed Mr Blair's "equivocation" on the issue was giving "comfort and encouragement to homophobes".