DUP accused regarding royal marriage reforms stance

But today the nationalist SDLP accused Mr Donaldson – whose role in the power-sharing government at Stormont includes promoting community relations – of repeating tribal myths.

Mr Donaldson said he was defending legislation that was key to the monarch’s constitutional position.

But SDLP deputy leader Alasdair McDonnell said: “Jeffrey should learn some proper history and drop the tribal mythology.

“Catholics owe no political or constitutional allegiance to the Pope or to the Vatican State and they never have.

“This was the lie that was used to attempt to justify the Penal Laws and the legal definition of Irish Catholics as Papists, terminology that leading DUP members have only dropped in recent times.”

The South Belfast MP said the allegations that Catholics had divided loyalties was “poisonous 16th century propaganda”.

But Mr Donaldson defended his comments and said changes to the law could cause constitutional difficulties.

He said: “A potential monarch who would be a Roman Catholic and a member of that Church is required to owe their first allegiance to the Vatican.”

Mr Donaldson added: “There is therefore a potential conflict of interest.”

The Lagan Valley MP said: “Alasdair McDonnell should check his facts before he makes these kind of comments.”

He said the SDLP could help boost community relations by asking the Vatican to overturn claims that Catholicism is the only true Christian Church and recognise the status of other Christian denominations.

He told Mr McDonnell: “That would be a useful step rather than tampering with legislation that protects the constitutional position of the country.”