A major shake-up of adoption law in Scotland, which would see gay and lesbian couples able to adopt children for the first time, is under attack from a Scottish Nationalist.

Roseanna Cunningham, an SNP member of the Scottish Parliament, has tabled a motion which would prevent gay couples from adopting. The new legislation will be debated at Holyrood today.

Under the new arrangements proposed by the Scottish Executive, gay and lesbian couples, as well as unmarried straight couples, will be eligible to jointly adopt children.

Currently only 400 children are adopted in Scotland every year, while 6500 remain in care.

The Catholic Church, still a powerful voice in Scotland, has led the campaign to try to stop the new law.

Ms Cunningham, the MSP for Perth and a former candidate for SNP leader, denies she is homophobic.

“This is not about gay rights, this is about children and for me the evidence shows that children do best in what we call a traditional family setting.

“That’s what we should be seeking to replicate for children who have lost their parents,” she told the BBC.

The SNP, while a marginal force in Westminster politics, are the second-largest party in the Scottish Parliament. The rest of the party are expected to vote for the new adoption arrangements.

The Scottish Green Party said it would support the rights of gay and lesbian people. Green MSP Patrick Harvie told the BBC: “Children brought up in a loving relationship do better, children brought up in a stable family environment do better – that’s very clear – but that doesn’t mean that marriage is the only acceptable model.

“The question for the state and for society is how best do we support all families to do the best job they can.

You don’t do that by simply saying that some families are second class.”

The bill will be debated today and is expected to pass.