LGBT+ rights campaigners march through Belfast against the ban on same-sex marriage. (Getty)

An anti-LGBT+ Christian group has threatened to take legal action over the extension of same-sex marriage to Northern Ireland.

Gay weddings are set to begin in the region on Valentine’s Day, after Westminster moved to extend equal marriage to the region in the absence of a devolved parliament.

However, London-based evangelical lobbying group Christian Institute has said that Northern Ireland secretary Julian Smith could face legal action if there is not an immediate move to bring forward “free speech protections” for opponents of equality in the region.

Christian Institute threatens legal action over equal marriage.

The group’s deputy director Simon Calvert claimed in a release: “I am extremely concerned that Northern Ireland’s unique public order law could get in the way of free speech and debate about gay marriage.

“In the run up to same-sex marriage coming into law, I’d expect lots of churches to be preaching in support of traditional marriage and against same-sex marriage.

“We don’t want the police using public order law to try to punish ministers for preaching the bible and arrest them for what they say from the pulpit.”

He added: “People will speak plainly on both sides of this issue. It must be a free debate and a free-flowing exchange of ideas, not a spectacle involving people being arrested.

“Even if these arrests never lead to a prosecution, the chilling effect would be huge.

“So we need clear protections for free speech written into public order law in Northern Ireland – just like they were in England and Wales before gay marriage was introduced there.”

Claims dismissed as ‘scaremongering’.

However, LGBT+ campaigners dismissed the claims.

Solicitor Ciaran Moynagh of the Love Equality campaign dismissed the group’s claims as “scaremongering.”

He told the Irish News: “The new law is clear. Religious ministers of any creed are free to preach. Hate speech, of course, is a totally different thing. It has no place in churches or society as a whole anyway.”

A spokesperson for the UK government’s Northern Ireland Office said: “As the Secretary of State announced in parliament in October, a public consultation on same-sex religious marriage in Northern Ireland (and the associated protections), as well as conversion entitlements, is being prepared for publication, subject to confirmation by the government.”