The Church of Scotland's annual General Assembly is set to debate the ordination of gay ministers today, May 21, in Edinburgh.

Last year's Assembly concluded that the Church could not condone same-sex marriages or civil partnerships, however commissioners voted in favour of a proposal that would allow individual congregations to 'opt out' of the Church's official policy on homosexuality, and could choose to employ a gay minister should a vacancy arise.

This decision has caused significant division among Christians across Scotland, and many congregations have opted to leave the Church of Scotland; choosing instead to join the Free Church, which has a firm stance against homosexual clergy.

Just this week the Kirk's largest congregation on the Western Isles, Stornoway High, has split, with 250 of its 350 members choosing to worship under the banner of the Free Church.

"Sadly our congregation could simply not identify with the general direction the Church of Scotland is headed in, and the sensible option was to leave," explained Christopher Martin, Stornoway High's former session clerk.

In the past year, eight Church of Scotland ministers have made the switch to the Free Church. David Robertson, a Free Church minister in Dundee and director of the Solas Centre for Public Christianity, says it's a trend that's likely to continue.

He says that some conservative members of the General Assembly will today call on the Kirk to "reaffirm the biblical position on same-sex marriages...but it's unlikely to be accepted".

"In reality, most people now don't expect the Church's position to change, and as a result a number of congregations have left, and more will leave in the next year," he told Christian Today.

"Some conservative evangelicals will stay and accept the situation, but not the theology behind it, but there will be other congregations who will leave.

"The Church of Scotland will say only one per cent of congregations have left, but it's a drip, drip, drip effect. The Church is losing 20,000 people a year and there's no sign of that trend being reversed; it will only accelerate," Robertson contends.

The loss of so many members is having a significant impact on the life of the Church in Scotland. Robertson labels a lack of young people deciding to train for ministry as a "big crisis".

"They are debating whether it's to do with costs or length of time for training, while in reality is the biggest factor is one they're not looking at – there are a significant number of young men going into ministry in Scotland, but they're going into more robust churches," Robertson said, noting that one free church has two young men training for ministry, while the whole of the Church of Scotland has only two men in their 20s heading for ordination.

"I don't think it's precisely because of the civil partnership issue, but I think it's primarily because the Church is moving away from a more biblical theology," he insists.

"The Church is driving people away; it's largely been taken over by the theologically liberal, and conservative evangelicals are permitted only if they don't rock the boat. On the one hand it's a broad Church, but then it's like 'If you don't agree with us, you should be out'."

Robertson finishes: "Last year the General Assembly reaffirmed biblical teaching that same-sex civil partnerships are wrong, but then allowed ministers who are gay in. It confused people, and made a laughing stock of the Church here. They meant well, and I'm sure thought it was a brilliant compromise, but it can't work – you can't say it's wrong but we'll let you do it anyway".

Rev Jeremy Middleton of Davidson's Mains Parish Church in Edinburgh will urge the Assembly today to support the notion that "marriage between one man and one woman is the only right and proper context for sexual relations".

Under his proposal, clergy in same-sex partnerships will be banned from serving the Kirk, though celibate gay ministers will not. It is thought that the Assembly will not approve this suggestion, however.

The Assembly will close on Friday May 23.