The leader of the Roman Catholic Church in Scotland and the most senior Catholic in the UK has declared “war on gay marriage” pledging to spend another £100,000 in its campaign against equal marriage rights for same-sex couples in Scotland.

Speaking in today’s Sunday Times, Cardinal Keith O’Brien warned the Scottish Government that it will face an “unprecedented backlash” from the Catholic Church in Scotland if it goes ahead with plans to legalise same-sex marriage, claiming “marriage is under threat and politicians need to know the Catholic Church will bear any burden and meet any cost in its defence.”

The Catholic Church says it will spend an additional £100,000 on an advertising campaign against the plans, on top of the £50,000 it has already spent against marriage equality in Scotland.

The Equality Network, the LGBT equality charity that campaigns for equal marriage, slammed the move as “aggressive, undemocratic and unchristian” and urged the Scottish Government to “stand up for equality” rather than “give in to threats”.

The Equality Network says that the leadership of the Catholic Church in Scotland has a wider “anti-gay agenda” pointing out that in addition to opposing same-sex marriage the Church previously ran expensive campaigns against the equal age of consent, the repeal of Section 28, civil partnerships, and same-sex adoption.

Previously Cardinal O’Brien has described same-sex marriage as a “grotesque subversion”. In December, he said the introduction of Civil Partnerships had been a mistake, arguing the law should never ‘facilitate’ same-sex relationships; “These measures were not in the best interests of our society. The empirical evidence is clear, same-sex relationships are demonstrably harmful to the medical, emotional and spiritual wellbeing of those involved, no compassionate society should ever enact legislation to facilitate or promote such relationships, we have failed those who struggle with same-sex attraction.”

Tom French, Policy Coordinator for the Equality Network, said; “For the Catholic Church to spend another £100,000 fighting LGBT equality in its self-declared ‘war on gay marriage’ seems to be an aggressive, undemocratic and unchristian thing to do. At a time of financial crisis, when poverty and deprivation are on the rise, surely there are better things that this money could be spent on. We know that two-thirds of Scots, and a majority of Scottish Catholics, support same-sex marriage. We trust that the Scottish Government will make its decision based on democratic principles and the evidence, and not who can spend the most money. We urge the Scottish Government to stand up for equality and not give in to threats.”

The public consultation on same-sex marriage closed in December with over 50,000 responses. The Scottish Government is due to publish the results and announce its decision this month.

In June the Equality Network announced that a majority of MSPs had signed its Equal Marriage Pledge, committing themselves to voting in favour of same-sex marriage. 74 MSPs have now said they will vote in favour, whilst just 9 remain opposed.

Opinion polls have shown consistent public support for same-sex marriage in Scotland. The most recent poll was conducted in mid-June by Ipsos MORI on behalf of the Equality Network. It showed record support with 64% of Scots in favour of a change in the law, and just 26% opposed. Separate polls conducted over the past two years by Populus, YouGov, Angus Reid, and the Scottish Social Attitudes Survey, have all shown similar levels of support.

The Scottish Social Attitudes Survey also showed that a majority of Scottish Catholics support same-sex marriage with 57% in favour and just 25% opposed.

The Equality Network is committed to working with MSPs to secure a Members Bill if the Scottish Government decides against proposing equal marriage legislation.