A lawyer for a group of Northern Ireland politicians has accused the British government of being “cavalier” over the extent of its prerogative powers to trigger Britain’s exit from the European Union.

The submission was made by David Scoffield QC on the third day of the historic Brexit appeal at the Supreme Court in London.

Mr. Scoffield, who represents a group of politicians as well as others with close associations with the voluntary and community sector and human rights organizations in Northern Ireland, told 11 justices they are “concerned about how withdrawal from the EU will uniquely effect Northern Ireland”.

He told the court they want to “ensure the process of dealing with the referendum result is both lawful and properly considered”.

Mr. Scoffield said: “In our submission, the UK government’s contentions on the extent of its prerogative powers are, with respect, cavalier.”

The justices heard from Mr Scoffield that the case of those he represents was that the process following the June referendum should comply with the requirements of law – including that parliament should have the final say on whether an Article 50 notice is given, “and that Northern Ireland’s particular circumstances should be recognised and properly taken into account”.

Mr. Scoffield referred to the importance of international relations between Northern Ireland and the Republic which, under devolved powers, involved “agreements and implementation bodies”.

He said that in authorizing Article 50, the UK government would be “driving a wedge” between the north and the Republic.

An Article 50 notification could only be sent by the British government if authorized by an act of parliament.

And he argued that, before Article 50 was authorized, there was “a constitutional requirement” that the British government should first seek a “legislative consent motion” from the assembly.

The justices also heard argument on behalf of Raymond McCord, whose son was murdered by loyalist paramilitaries, and whose Brexit case surrounds the impact on withdrawal on the peace process.

His counsel Ronan Lavery QC said: “We say, as a matter of the constitution of the UK, it would be unconstitutional to withdraw from the EU without the consent of the people of Northern Ireland.

“It would be very disturbing for the people of Northern Ireland to imagine that the terms so agreed in the Good Friday Agreement were not binding and did not have constitutional status.”

He added it was “unthinkable” that the will of the people of Northern Ireland could be overturned by parliament against their wishes.