If gay marriage is legalised teachers and others could be forced out of their jobs if they fail to endorse such unions, a top lawyer says.

Parents would have no right to insist that their children are withdrawn from school lessons across the curriculum that approve of same-sex marriage.

Chaplains who work in the NHS or the Armed Forces could be dismissed if they preach that marriage is just between a man and a woman.

Foster carers could be barred from looking after children if they say they disagree with allowing two people of the same sex to marry.

And religious groups could be banned from using public buildings over their support for traditional marriage.

Leading human rights lawyer Aidan O’Neill QC has written a legal opinion on the civil liberty implications if marriage is redefined.