The gap between politics and the law is further exposed. But ruling on the clash between the Scots and Irish nationalists with the UK government will be the more momentous decision for the Supreme Court.

Northern Ireland lawyers divided before the UK Supreme Court over whether the consent of the NI Assembly was needed to take the province out of  the EU in the light of the majority vote for Remain. In a re-run of the arguments brought before Belfast High Court, the NI Attorney General John Larkin yesterday  dismissed the argument  ( p117) that by leaving the EU the UK Government was violating the consent principle of the GFA because a majority in Northern Ireland   had voted to Remain.

It ( the consent principle)  is entirely and exclusively about the status of Northern Ireland within the UK, and we say that not even the most daring exegesis  transforms the provision that is addressed solely to the status of Northern Ireland as  part of the United Kingdom into a provision that is also  somehow about the EU membership of the United Kingdom.

The SDLP leader Colum Eastwood attacked Larkin’s submission because he seems to believe his case is legally correct – contrary to what the NI High Court found, calling it  “abdication of responsibility”.

He said the Scottish government’s Lord Advocate James Wolffe was at the hearing under the direction of the Scottish government and was representing its will.

“Why is our own attorney general not advancing the expressed will of the people of Northern Ireland who voted to remain in the EU,” the Foyle MLA said.

Mr Eastwood said Sinn Féin needed to tell the public whether the party were briefed by the attorney general in advance of his Supreme Court appearance.

“He was jointly appointed by them, they cannot wash their hands of responsibility for his actions,” he said.

One difference of course is that the Executive parties are divided on EU membership and therefore have no government policy on it, where as the SNP’s position is  unambiguously  against Brexit.

Today counsel for the two Northern Ireland cases opposed the government’s right to trigger Article  50 without approval,  but on different grounds.

David Scoffield QC appearing for the NI Green Party  leader Steven Agnew  accused the government of being “cavalier” with its attempt to use the royal prerogative, given the effects he says it would have on the devolution settlement.

The Northern Ireland Act 1998 giving effect to the Belfast agreement  involved co-operation with the Republic of Ireland.

Continued membership of the EU is an integral part of the act.

The  government would be driving a wedge between Northern Ireland and the Republic of Ireland by triggering article 50. Even if breaking faith with some of the north-south agreements is a domestic matter, that is something that must be done by a legislative consent motion, not just an act of parliament.

If legislative consent is sought, it may be granted ..what we are asking the court to clarify is whether and how the convention is engaged.

Ronan Lavery QC for Raymond McCord went much further. He argued that sovereignty had already been transferred to the people by the Northern Ireland Act 1998 which implemented the GFA.

Section 1 of the NI Act transferred sovereignty to the people of Northern Ireland over any kind of constitutional change. The sovereignty of Parliament  has now gone.”

To the extent that the UK no longer has a written constitution we say that the Good Friday agreement forms part of the Northern Ireland constitution…

It would be very disturbing for the people of Northern Ireland to find that the terms agreed in the Northern Ireland agreement were not binding, had no constitutional basis.

The triggering of article 50 would impede the principle of self-determination.

It would be unconstitutional to withdraw from the EU without the consent of the people of the Northern Ireland.

It was left to James Wolfe QC  the Scottish government’s Advocate General, to make the case for the consent of the devolved legislatures for withdrawal.

English law like Scottish law precludes the government from changing the law of the land through use of the prerogative, said Wolfe.

The Scottish government does not have a veto on whether the UK leaves the EU but its consent for effects on its citizens must be sought and is of constitutional significance.

Wolfe said there was  plenty of evidence including statements by the UK government as to the importance of the “Sewell convention” which says that the devolved governments must be consulted on devolved matters of significance by the UK government before it legislates.

The Scotland Act 2016 says “ normally” consult but Wolfe thought this was “not justiciable.”

Lord Mance however said  conventions like Sewell while  important but not legally binding.

The UK government decided to enshrine it into law because of its importance, answered Wolfe.

This exchange goes to the nub of the constitutional arguments affecting Scotland, Wales and Northern Ireland and their  differently evolving relationship with UK central.

If the UK government introduced a brief Bill to trigger Brexit the issue of Holyrood’s  consent supported by the votes  of the 54 SNP MPs at Westminster would go active. The consequential devolution of powers over agriculture and fisheries, the environment and workers’ rights  straight  from Brussels to  Holyrood could also come into play. It could all get very complicated and feed  demands for a second  indyref.

Before Brexit the Supreme Court  was hoping to avoid having to rule on clashes between devolution and Westminster.  Over Brexit this  may now be unavoidable, although the Court must be hoping that developments in politics will ease their burden of decision.

The principal case presented by Lord Pannick QC. was that the government had no power to quit the EU without the consent of the “sovereign” Westminster parliament.  He did not deal with the role of the subordinate legislatures.

Today Lord Pannick was challenged by the President of the Supreme Court Lord Neuberger to explain  why he maintained  that the 2015 Act instituting the Brexit referendum had “ no effect” in law  in triggering Article 50 to quit the EU,  while conceding that politically it obviously did.   Neuberger asked if the court did not have to look at the consequences of the Act as well as its wording which was silent on how to implement the referendum result.  Parliament and the government through the Act may have delegated the decision to the people. “It would be surprising if the referendum had no legal effect”.

On the other hand the Referendum Act did not make the result legally binding and it could have if the government had wanted it to.

Here Neuberger got to the nub of the main issue. His question suggests that the Court will also  have important things to say about consent  to Brexit by Scotland and Northern Ireland.

Interestingly part of the basis of Neuberger’s question was a ruling of the Law Lords (the predecessor of the Supreme Court) headed by Lord Bingham in the Robinson case in 2002 in which Peter Robinson for the DUP challenged the redesignation of the Alliance party as “ unionist” in order to keep the Assembly in being without an early  election which would have resulted in its suspension or perhaps dissolution.  Here is part of the law lords’ momentous decision by three votes to two, delivered by Lord Bingham who was regarded as one of the UK’s greatest judges. Bingham  boldly  adopted a creative  approach beyond the letter of the law to take account of changing circumstances of government that may commend itself today.  For critics of Supreme Court activism however,  a move of this sort today over Brexit would bring a fresh  avalanche of criticism down upon their heads.

        The 1998 Act does not set out all the constitutional provisions applicable to Northern Ireland, but it is in effect a constitution. ..

Where constitutional arrangements retain scope for the exercise of political judgment they permit a flexible response to differing and unpredictable events in a way which the application of strict rules would preclude..  I conclude that the Assembly had power to make a valid election even though the six-week period prescribed under section 16(8) had expired, that the election of Mr Trimble and Mr Durkan on 6 November 2001 was lawful and that in the unusual circumstances of this case the Secretary of State was entitled to propose as the date for the poll for the election of the next Assembly a date already fixed by section 31(2) of the 1998 Act.

Robinson reared its head again in the Brexit case particularly over that key phrase of Bingham’s –       (“ flexible response”).  Coincidentally, counsel for Peter Robinson was John Larkin, now the NI Attorney General. Little did he think then that the Robinson case would be invoked in a case of such overall fundamental importance.