In 1981, Harvard academics William L Ury and Roger Fisher published “Getting To Yes”. The title may seem nail-gratingly American – recalling huckster treatises ghost-written for certain fast-and-loose leaders of the free world – but this slim volume outlines what Fisher and Ury characterize as a “principled” approach to negotiations. And heaven knows, UK politicians could do with all the advice they can get.

People, Fisher and Ury argue, often misconstrue good negotiating as a frowning contest. Zero sum, win-lose – they argue too many of us see the negotiating as a simple matter of who has the deepest brows. We think the winner is whoever frowns last and frowns longest.

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In some scenarios, of course, a tough approach is perfectly serviceable. Try to persuade me to have dinner in a vegetarian restaurant, and I’ll show you the true meaning of bloody-minded cussedness. Inflexible wheeler-dealers beat softer, more accommodating bargainers every time. But what happens when two hard-heads clash? All that is generated, Ury and Fisher suggest, is impossible impasse. Talks break down. Opportunities for mutual gains are missed. Recriminations continue. They suggest a laser focus on positional bargaining can leave you splitting the difference when a better deal is possible, alienating your interlocutor with personal attacks and tough-guy nonsense in the process.

I defy any fair-minded observer to contemplate the UK Government’s approach to Brexit and not to see parallels with Fisher and Ury’s account of the diddy negotiator. Two of the duo’s more helpful concepts are the BATNA and the WATNA. Your BATNA is the Best Alternative To a Negotiated Agreement. If a deal makes you worse off than the alternative – by all means, avoid it. Your WATNA, by contrast, focuses on the downside. What’s your Worst Alternative to striking a deal? Theresa May’s administration seems to have been living in denial about the gruesomeness of its Brexit WATNAs and its BATNAs for some time. This week, she was forced to confront the domestic implications.

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Introducing the Scottish Government’s Brexit Continuity Bill, Mike Russell frankly described one set of outcomes the PM must contend with. Yesterday, Mr Russell outlined a three week timetable for the legislation, arguing that Holyrood “must prepare itself to assert, if it has to, the right to legislate for itself the devolved consequences of EU withdrawal” adding “it is simply not acceptable for Westminster to unilaterally re-write the devolution settlement and impose UK-wide frameworks in devolved areas without our consent.” On this timetable, if a majority can be found at stage three, the Continuity Bill will pass as early as March 21, hostile weather fronts permitting.

As the Lord Advocate – James Wolff QC – told the chamber this week, the Presiding Officer’s critical take on legislative competence of Mr Russell’s Brexit Continuity proposals “does not prevent this Parliament from considering and, if so advised, passing the bill.” Wolff’s argument on competence is bracingly simple. If the Scottish Government’s continuity Bill “is incompatible with EU law,” he argues, “the same reasoning would apply equally to the UK Government’s bill.”

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The law officer quipped to MSPs this week that he has “spent a lot of time” in his “professional career avoiding hypothetical questions.”

But we can be reasonably clear about the UK Government’s still hypothetically but increasingly unattractive range options about how to deal with ongoing Brexit trouble north of the Antonine Wall and west of Welsh Marches.

Consider the escalating crisis from May’s perspective. She knows – or ought to know – several important things. Firstly, she knows that Holyrood has rejected David Davis’s Bill as “incompatible with the devolution settlement.” She knows that her Scottish Tory colleagues support this line. This isn’t sanctioned dissent: it is the real thing. The PM must also know that ratting on promises to fix the Bill can only cause these colleagues acute political discomfort – forcing Ruth Davidson and her colleagues into either a shaming reverse-ferret, or to double down on their earlier position in the teeth of the intransigence of UK party colleagues, with all the political bloodletting and anxiety that must occasion.

May must also know there are the votes in Holyrood to pass the Scottish Government’s Bill, irrespective of the presiding officer’s analysis of its legislative competence. Fourthly, she also knows that if the Holyrood majority backs it, the Presiding Officer must forward the Bill to the monarch for royal assent, irrespective of his own legal qualms.

The Prime Minister must also understand that, under the Scotland Act, her law officers have four weeks to intervene to prevent the legislation from reaching the statute book by referring it to the Supreme Court for their final word on whether James Wolffe or Ken Macintosh has the better legal theory.

The consequences of such an intervention are uncertain – but you can sketch out a few ideas of what is likely to happen if she instructs Baron Keen of Elie to interpose himself into the Scottish parliamentary process.

If the justices uphold the Lord Advocate’s legal analysis and rule against the UK Government – the PM is stuck with Scottish and Welsh continuity Acts, no deal on how to approach devolved frameworks, and in the process, will have handed the devolved administrations a mighty propaganda victory.

Alternatively, the UK Government might win their legal challenge – but there is political hay for Holyrood and the Senedd to make here too, underscoring the continued indifference of the centre to devolved interests, whatever the fine tooled text of the Government of Wales and Scotland Acts might say. Sayonara the “respect agenda”. Cheerio, even the ghost of May’s commitment – back in July 2016 – to “securing a UK wide approach” to Brexit.

Even with a pyrrhic legal victory in hand, the PM would still be left with the problem that devolved consent is constitutionally necessary to get her Brexit Bill through. And it seems unlikely, to put it diplomatically, that spiking devolved legislation would foster much in the way of goodwill.

The PM must also know that even if she doesn’t instruct her Advocate General to call in Mike Russell’s Bill – any aggravated Brexit-loving punter with an axe to grind and money to burn will be able to do so. And worse, a legal challenge launched by a member of the public wouldn’t start and end in the Supreme Court, but have to wend its way slowly up the Scottish judicial hierarchy, the outcome of the case uncertain. This is a damned messy, ill-tempered way to govern.

In her back pocket, of course, May has Westminster’s parliamentary sovereignty which would allow a London majority to ram through David Davis’ Bill whatever MSPs and Welsh AMs make of it – but she also knows it is increasingly doubtful the House of Lords would support her legislation with the democratic assemblies of Wales and Scotland in open dissent.

Whatever way you look at it, this has all the hallmarks of a comprehensively unpleasant political predicament for the PM. Theresa May’s BATNA and her WATNA both look awful.

Meanwhile, the Scottish Tories are left looking greener and greener about the gills. And no wonder. Adam Tomkins persuaded his colleagues into a courageous position on David Davis’s Brexit Bill, joining the cross-party consensus in Edinburgh that its approach is “incompatible with the devolution settlement.”

More than anyone, Tory MSPs need the UK and Scottish Governments to strike a deal if they are going to avoid being mown down in the political crossfire. But the costs and the discomfort of their position are mounting. This week, Professor Tomkins tells us that “the UK and Scottish Governments are within spitting distance of agreement” – though for folk who are not privy to private conversations between the governments of these islands – there seem precious few clues yet than we are on the cusp of a meaningful accord. May and her administration have only themselves to blame for the slow-motion toboggan crash this has – all too predictably – become.