Nicola Sturgeon will presumably try to hold a vote on Brexit in the Scottish Parliament at a moment that suits her – in other words, one that will best maximise, as she sees it, support for Scottish independence, thereby paving the way for a second referendum on the matter.

Her five tests for Theresa May’s Government to pass are clearly framed so that they can be judged to have been failed.  (They include safeguarding free movement of labour and access to the Single Market, which some believe would necessitate a hard border between Scotland and England,)

As matters stand, she may struggle.  Recent polls show support for Scottish independence falling.  The drop in the price of oil, and the prospect of being outside both the EU and the UK, seem to be taking their toll.  But this is where the Supreme Court comes in.

Since the Government’s defeat in the High Court, the Scottish Government has joined the case.  James Woolfe, Scotland’s Lord Advocate, argues in a submission to the Supreme Court that moving Article 50 would affect the legislative competence of the Scottish Parliament.

It therefore follows, he claims, that if the Government is to move the article in London, then a legislative motion is also required in Holyrood.  Were to court to uphold his view, it is easy to see what would follow.  Sturgeon would declare her tests unpassed, and the Scottish Parliament would vote against Brexit.

It has no power, of course, to over-rule whatever the Government or Parliament in Westminster decide to do.  But that is beside the point – which is that the highest court in the land would have decreed that MSPs must vote on Brexit, and they would duly oppose it.

Sturgeon would then be in a position to whip up pro-indepedence sentiment, and try to get those polls on a second referendum moving back in her direction.  She might succeed, and might not.  But such a verdict by the Court would risk reviving the campaign to break up the United Kingdom.

It’s worth noting that the court will also be hearing another crucial case – two appeals against the verdict of the High Court in Northern Ireland which decided, contrary to the High Court in England, in favour of the Government’s position on Brexit.

If the Government loses the Miller appeal, it may not get a Brexit Bill through Parliament in time to meet its March 31 timetable: much depends on when the judges produce their verdict.  But it is convenient to Ministers that the cases are being heard before the bill commences, which may explain their insistence on proceeding as they have.

So, then.  If the Government loses the Northern Ireland appeal, a constitutional crisis would be sparked.  For how can one part of the UK stay in the EU while the other three parts leave?  Experts reportedly consider such an outcome unlikely but, to paraphrase Michael Gove, experts are sometimes wrong.

And if the court rules that a comprehensive replacement for the European Communities Act of 1972 is required before Article 50 is moved – a possibility floated by Lady Hale, one of the judges who will rule on the appeal, in a lecture abroad – the Government’s Brexit timetable could go bust.

In such an eventuality, Brexit might take place after the 2020 election and not before it, which would open the door to the poll overturning the referendum result.  This is unlikely, given Labour’s present policy stance, but one can’t be sure.

But in any event, it is the possibility of the court declaring that a legislative motion is required in Holyrood, and the Scottish Parliament then voting against Brexit, that will concentrating Ministers’ minds most.  If it comes to pass, the Government will have three options.

  • Ignore the vote altogether, and press ahead with Article 50.  This would risk boosting pro-independence support north of the border, and paving the way for a second referendum on Scottish independence, which might be won.
  • Back down.  Which could mean dropping Brexit altogether or, more likely, signing up to Single Market membership – and, in consequence, abandoning any credible attempt to cut EU migration.  This would be a gift to UKIP and Nigel Farage, and split the Conservative Party.
  • Call a general election.  Not so easy, of course, given the Fixed Terms Parliament Act.  But not impossible, either.  And a poll would probably confirm – though “Who Governs Britain?” polls have an unhappy history – that the UK wants out of the EU.  But were Ruth Davidson’s candle of Tory revival to be snuffed out in Scotland, such an election might simply entrench the two countries’ positions.  What would happen then?

P.S: Experts apparently consider it unlikely the court will rule in favour of Scotland’s Advocate-General.  But I cited Gove earlier on experts, and do so again now.