A COLLEAGUE has a drinking crony with a standard quip. To explain away any incomprehensible development in public or private life, the barfly invariably invokes “legal reasons” with a nod and a wink. It’s an explanation that covers a multitude of sins and who can blame him for using it? To the average punter, the internal workings of the law’s infernal machinery often seems baffling. “For legal reasons” is often as good and as comprehensive an explanation as any.

So it goes with the legal tidings this week that Theresa May’s Attorney General has decided – in cahoots with the Advocate General for Scotland – to elbow Holyrood’s Brexit Continuity Bill off the Queen’s desk and into the docket of the UK Supreme Court. Hold on, ma’am, Advocate General Lord Keen of Elie says. We think Holyrood – and the Welsh assembly – have nicked our powers.

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Giving evidence at the Scottish Parliament back in 2015, I remember Tavish Scott was affronted at my suggestion that vagueness in the devolution settlement might generate litigation between the different administrations at work in these islands. “Governments do not go to court against each other, do they?” the LibDem MSP asked, insisting such litigation was unthinkable.

Come 2018, one thing is clear: they do now. But Mr Scott’s question was more fundamentally misinformed. There’s a statutory obligation in media reports to refer to the UK Government’s case against the continuity bills as “unprecedented” – but that isn’t quite true. While Whitehall has avoided referring Scottish bills to the Supreme Court since 1998, the Welsh have grown rather more familiar with defending the legality of their measures in front of the court. The scores on the doors are two-to-one in favour of Carwyn Jones’s administration. The UK Government now has a chance for a score draw.

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They took up the opportunity late. Attorney General Jeremy Wright waited till the last moment to lodge his papers. Why? From the UK Government’s perspective, the timelines are a mess. Negotiations with the devolved administrations on David Davis’s proposals remain deadlocked. The Lords will shut the book on his bill on May 8. If Davis wishes to table amendments with the blessing of the devolved governments, a deal must be struck with Nicola Sturgeon and Jones before then.

When Holyrood passed its Continuity Bill in March, by 95 votes to 32, Theresa May had just four weeks to refer the case to the Supreme Court. Since then, senior Scottish Tories have been softening up public opinion for the possibility of litigation. The Secretary of State for Scotland was doing his best to appear intensely relaxed about negotiating with Holyrood against the backdrop of an exchange of lawyers’ letters last week. “I think when you have two different views as to the legality of the bill, it’s almost inevitable that it has to be tested in the legal process,” David Mundell said, characterising the case as just “a process thing”.

Well, yes and no. First, let’s be clear what this case isn’t about. It isn’t about the Sewel convention or Holyrood consent. It isn’t about the Act of Union. Whatever the outcome, it will not transform the UK into a federal state. So what’s the heart of the case? Ultimately, the devolution legislation requires several things of its parliaments. They must respect fundamental rights. They must not pass laws about matters reserved to Westminster. And, critically, they are not entitled to pass laws which are “incompatible with EU law”.

The core of the UK Government’s argument is that the two devolved legislatures are doing precisely this with their continuity bills. This argument has considerable weaknesses. Firstly, it is not contrary to EU law for a member state to contemplate departing from the jurisdiction of the European Court. Article 50 sketches the roadmap for departing.

Lord Advocate James Wolffe QC’s argument has a droll sting to it. If laying the legal groundwork for Brexit in Holyrood is incompatible with EU law then, logically, David Davis is also acting incompatibly with EU law in trying to steer his leaky Brexit Bill through Westminster. In Andy Wightman’s parallel Court of Session case on the revocability of Article 50, May’s lawyers built their case around the idea Wightman’s challenge was “hypothetical and academic”. Why? “The UK Government’s policy was that the notification will not be withdrawn.” But in challenging the continuity bills as unlawful power grabs by the devolved parliaments, Lord Keen wants to persuade the Supreme Court that Brexit isn’t a done deal.

So what’s the argument? That Westminster can legitimately anticipate the slow-motion car-crash of withdrawing from the EU, but Holyrood and Cardiff are obliged to wait for the impact before reacting? Schrodinger’s Brexit, at once inevitable and hypothetical at the same time? Feel the cognitive dissonance. Wibble, wibble.

Moreover, the Lord Advocate was wise to the obvious objections, anticipating noises about legislative competence, so Holyrood’s bill sets out chapter and verse that its purpose and effect is to make provision for what happens after the UK “takes back control” and the monochrome red tape of Brussels is rebranded red, white and blue.

The Continuity Bill’s provisions can’t kick in until “exit day”, meaning the day the UK leaves the EU. Yet despite these caveats and reservations, Richard Keen is determined to argue the devolved bills trespass into EU law. He’s also likely to dredge through Schedule 5 of the Scotland Act looking for reserved matters that can be thrown the Continuity Bill’s way if his EU argument fails. Belt and braces.

Publicly, the Scottish Conservatives have been on full trumpet about the continuity legislation. Illegal Bill. Rule of law. Presiding officer’s opinion. Nationalist grievance-mongering. You know, the usual Tory bingo. But privately, there is recognition that the legal issues with the Bill are more finely balanced, and there is every chance Keen will lose his case.

On the face of it, you might think there are only two outcomes – win or lose – but it isn’t quite so simple. The Supreme Court might reach the conclusion the bill is an overstretching of Holyrood’s powers

Alternatively, the justices may decide Cardiff and Edinburgh are well within their rights to lay the legal groundwork for how to reckon with EU law in devolved areas after Brexit. For the UK Government, this outcome has obvious embarrassing political potential.

The PM’s law officers have been keen to present their constitutional manoeuvres on the Bill as a publicly-minded attempt to ensure legal certainty for businesses and punters about who decides what in the wake of Britain’s departure from the EU. But in the hurly-burly of politics it can readily been framed as an attempt, as Joanna Cherry put it, “to defeat a bill in the courts which it couldn’t defeat by democratic means in the Scottish Parliament”.

But for the UK Government, there is also a sticky third option. The Supreme Court might decide the detail of the emergency bills passed by the Senedd and Holyrood are outside their legislative competence – while accepting in principle that devolved parliaments are entitled to track their own course out of Brexit within their powers.

For Theresa May, this looks like a decidedly Pyrrhic victory. That’s the law, but the backdrop remains political. Come what may, this case is another mess, another ugly scene on Brexit’s Via Dolorosa, and for Mrs May’s administration and its Whitehall worldview, another unforced error.