PHILIP Hammond is a chatty bloke. The Chancellor’s demeanour may be dry as ash but, give him his due, he can fair rabbit on. Briefing the press in Edinburgh on Thursday, the words came tumbling out, most of them unhelpful to Nicola Sturgeon.

The First Minister’s plan for a bespoke Scottish deal for Brexit was “impractical” and “not a realistic prospect”, said Mr Hammond. “I look forward to us moving on from this slightly backward-looking, clutching-at-straws, trying-to-resist-the-ill-of-the-people [attitude].”

He was very clear. There would be no separate arrangement for Scotland or any other part of the UK on Brexit. When the UK enters withdrawal negotiations with the EU27 next year, it will be with a one-size-fits-all approach.

However, there was one subject on which Mr Hammond dried up. Asked if MSPs should have a say on triggering Article 50 through a legislative consent, or Sewel, motion (LCM) if Westminster legislates on the issue, he declined to comment, merely saying it was a matter for the courts. He was referring, of course, to the 11 justices of the UK Supreme Court who will sit next week to hear the UK Government’s appeal on whether Theresa May can trigger Article 50 using the Royal Prerogative, or whether Parliament must give its approval.

The Government lost in the High Court, which said only Parliament can undo Parliament’s laws, a clear-cut decision that is unlikely to be overturned. The Scottish Government also has a dog in the fight. Ms Sturgeon’s most senior law officer, the Lord Advocate James Wolffe QC, will argue that not only should Westminster legislate, Holyrood should also have its say through an LCM, as Brexit affects the competence of Scottish ministers and of the Scottish Parliament, and a wide range of devolved policy areas.

This is where it all gets very interesting politically. Pro-Remain MSPs could not block Article 50 by refusing to pass an LCM as Westminster remains sovereign. If MSPs rejected an LCM, Westminster could ignore them. It is a convention, not an obligation. The Scotland Act 2016 says the UK Parliament will not “normally” legislate in devolved areas without Holyrood’s consent, but “normally” is an elastic term. In the classic sense, there is no veto. But this isn’t just about the law, it’s also about politics. If the UK Government refused to grant an LCM or granted one but refused to heed Holyrood’s decision, it would open a constitutional can of worms and bring the devolution settlement into question.

Going by the way the UK Government is urging the court not to endorse an LCM, on the basis the EU is a reserved matter of foreign affairs, it is clearly alert to the dangers. This issue was recently explored by the Commons Select Affairs Committee.

Michael Keating, Professor of Politics at Aberdeen, argued the classic view of Westminster sovereignty had been changed by devolution. Incorporating the Sewel convention into law was “either utterly meaningless or it means something, and if it means something it is part of the constitution”, he told MPs. “There is that weasel word ‘normally’, but again if ‘normally’ means whatever the Westminster Parliament at any time says normally is, you are emptying that of meaning. If these agreements have any meaning at all, it is that the Westminster Parliament can no longer simply say, ‘We are absolutely sovereign to do everything’.”

He was backed up by Dr Tobias Lock, a senior lecturer in EU law at Edinburgh University, who said the unwritten British constitution must be understood as “a political constitution first and foremost”. Westminster could always act unilaterally if it chose, but that would come at a “high political price”. If you defined legality or constitutionality as “what can be done without the courts interfering” Westminster could plenty. But if, more sensibly, you define it as what can be done “without political mayhem breaking loose”, then Westminster is more constrained.

So while the Chancellor’s refusal to grant a bespoke Scottish deal has shut down one option for Ms Sturgeon, the ramifications of Brexit mean she is not out the game yet. As there is no happy way to reconcile the Scottish Remain vote with the English Leave vote (appeals to the United Kingdom simply divide people all over again), some kind of constitutional crisis seems inevitable. And every politician knows never to let a crisis go to waste. It may be over the lack of an LCM or the high-profile dismissal of one, but the First Minister still has a chance to influence Brexit. After the Chancellor had stopped rabbiting, other hares remained running.