SCOTLAND's most powerful Catholic will speak today at the launch of a new alliance forged in opposition to proposals that could allow homosexual couples to be married in a place of worship.

Cardinal Keith O'Brien will address a rally organised by the Scotland for Marriage campaign, which has been set up as consultation continues on gay marriage and religious ceremonies.

The Catholic Church in Scotland has joined the Church of Scotland, the Christian Institute, which promotes the Bible as "the supreme authority" of all life, and other evangelical groups to oppose moves to give homosexual couples the same rights in marriage as heterosexuals. Currently same-sex couples can have a civil partnership carrying full legal rights, but the ceremony cannot be conducted in religious premises.

The Catholic Church has made a series of strongly worded attacks on the proposals which come after 61% of Scots said in a recent Social Attitudes Survey that same-sex couples should have the right to marry. Nineteen percent disagreed.

Cardinal O'Brien said: "As an institution, marriage long predates the existence of any state or government. It was not created by government and should not be changed by them. Instead, recognising the innumerable benefits which marriage brings to society they should act to protect and uphold it not attack or dismantle it.

"At the heart of this debate, however, there is one perspective which seems to be completely lost or ignored, it is the point of view of the child. All children deserve to begin life with a mother and father, the evidence in favour of the stability and well being which this provides is overwhelming and unequivocal."

Ministers said the plans would ensure religious organisations do not have to register same-sex marriages against their will.

Colin Macfarlane, director of Stonewall Scotland, which lobbies for equality for the gay community, said most same-sex couples would opt for a religious blessing as part of a civil ceremony and not a church service.

However, for members of the LGBT (lesbian, gay, bisexual, and transgender) community who observed a faith, the changes were of huge importance, he said.

Mr Macfarlane added: "The majority of people in Scotland do support same-sex marriage. When there are 1.2 billion people in the world living on less than a dollar a day, it's a shame that the churches' priorities are focused on preventing a few thousand people express their commitment and love for each other.

"It is the right of the churches to oppose same-sex marriage but it has to be done in a respectful manner."

Also speaking at the Holyrood rally is former SNP leader Gordon Wilson, and Ann Allen, former convener of the Church of Scotland's Board of Social Responsibility. Ms Allen said: "I'm confused as to why with so many pressing issues confronting us today in Scotland, our Government has chosen to prioritise time, effort and money on this particular issue. Canada legalised same-sex marriage in 2005 and today faces challenges to have polygamy legalised. Is this what we want for a modern Scotland?"

The event coincides with advertisements taken out today by Scotland for Marriage in three national newspapers, including The Herald, and which publicise the group's petition.