I couldn't pretend that I was seriously offended by the remarks of a former royal butler, and a glamour model I'd never heard of, on the Jeremy Vine show. Paul Burrell and the exotic Nicola McLean cast doubts upon Scotland's ability to survive as an independent country. “What do they have, a monster, oil, a lake (sic) ... Irn-Bru?”, they said. Well they would wouldn't they.

These empty-headed ruminations became headline news and clearly ruffled many Scottish feathers. It was probably the timing. The Vine show coincided with the Tory leadership campaign belatedly waking up to the Scottish question, following Holyrood's debate on the independence referendum bill.

Jeremy Hunt resorted to blood and soil nationalism of the kind the independence movement deplores. He said he had “Welsh blood, Irish blood, and spent two happy years of my childhood in Scotland”. So there. This mongrel circulatory system meant he would “NEVER allow our Union to be broken up”.

Boris Johnson didn't declare what blood coursed through his veins, though we can be sure that it's the purest sang d'anglais. He alternated between threats to “spike the guns” of the SNP, and mawkish appeals to Union solidarity. We are apparently “the awesome foursome”, which sounds like a superhero franchise gone bad. He too will never let the Union fall – or will he?

The unthinkable is being thought in the wider Conservative movement. Kevin James of the LSE wrote a powerful piece on ConservativeWomanHome arguing that a “Clean Brexit” can only happen if Scotland is allowed to leave the UK. He says a forthcoming parliamentary coalition between Nigel Farage and Boris Johnson (yes, I know) will lead to a dissolution of the Union.

I don't know if Boris has given much thought to the Scottish question. Since he hasn't devoted much intellectual energy to Brexit, one can assume that he's an absolute beginner on the constitution. But if and when he becomes Prime Minister (I can still barely write those words without an involuntary shudder), he's going to have to learn fast.

It's become a cliché to say that we are heading for a constitutional crisis, but we are. It is a multidimensional constitutional bourach that could leave the UK without a functioning government during its greatest crisis since the second world war. And lead to the break-up of the British state.

Everyone and his dog knows that the arithmetic is against Boris Johnson lasting more than a few days in No10. After the Brecon and Radnorshire by-election, and with the defection of Tories like Anna Soubry, the Conservative majority will dwindle to three, even with the DUP MPs. And they can't be guaranteed, since Arlene Foster's £1bn "confidence and supply” arrangement with Theresa May is about to expire.

The Tory membership must realise that there's a phalanx of Remainy Conservative MPs who loathe Boris and will vote against him in a confidence vote at the first opportunity. That's if Jeremy Corbyn can get his act together to call one. That means a general election in the autumn. Then, all hell breaks loose as the Brexit Party, the Liberal Democrats and the Scottish National Party tear into the carcases of the two old, divided parties: Labour and the Conservatives.

Britain will be in the realm of multi-party coalition politics, something to which the UK constitution is ill-adapted, presupposing as it does a two-party system of alternating governments of left and right. That no longer fits. The new alignment will be over Brexit and the deliverance, or otherwise, of Article 50. It is likely to be Brexit Party+Conservative versus Labour+SNP

The SNP, which could be returned with up to 50 seats, will be demanding a referendum on independence and ramping up demands to remain in the European single market. Many English Conservatives will say “bring it on” – 63% of Tory members told YouGov recently that they would be happy to see Scotland leave if that's the price of Brexit.

Boris Johnson, if he's still hanging around No10 playing wiff-waff on the Cabinet table, will suddenly discover that the United Kingdom is a misnomer. It is a Disunited Kingdom (as in my book of the same name, which I can't resist shamelessly plugging). Britain is not a unitary state in which parliament is sovereign, as it is in the text books. There is a new constitutional reality.

Antiquated constitutional authorities like Dicey waxed lyrical about parliamentary sovereignty and how Westminster's power is infinite. But for the past 20 years, powers have been ceded, first to the European Union, which has been legislating on trade matters on the UK's behalf for 40 years, and thereafter to devolved parliaments in Scotland, Wales and Northern Ireland (though the latter hasn't sat for a while).

Brexiteers have tried to ignore it, but the UK is really a multinational state in which regional parliaments exercise essentially federal powers. And no, I don't regard Scotland as a “region” either. Scotland is a nation, one of the two partners in the Union of 1707. But it is regarded as a region by Whitehall, and therein lies the problem.

Scotland never lost its national identity in the Union. It retained its kirk, legal system and education independently of Westminster. In the last two decades it has been in the process of restoring its economic and political autonomy, which had been ceded to the UK parliament in the 18th century. Brexit will force this into reverse, or force Scotland out.

Westminster is centralising power in order to extract the UK from the European Union, and create a UK single market to replace the EU single market. Boris Johnson's Global Britain has no place for a difficult pro-European Scotland. Nigel Farage will say to hell with Scots. It could be that, as in Czechoslovakia in 1993, the Union breaks first at the centre not the periphery. But a Velvet Divorce seems unlikely

I have never advocated an unauthorised (by Westminster) constitutional referendum in Scotland. But the increasingly aggressive unionism of the Conservative leadership is making the situation in Scotland critical. Support for independence has already risen to 49%, and 53% if Boris Johnson is PM. This can only increase as the Brexit crisis deepens.

Brexit has brought the inherent contradictions of the UK constitution to centre stage. A weight of history is bearing down on the UK at this most critical moment in its history. Scotland was never fully committed, heart and soul, to the Union. It was always a partnership of convenience, which placed Scotland as a junior partner in the British Empire.

After Margaret Thatcher and the deindustrialisation of Scotland, the ties became frayed. Devolution held things together, for a while. But eventually, the old Union became unsustainable, as the aftermath to the 2014 referendum showed. The SNP became the hegemonic force in Scotland.

Now, within months, there could be a solid majority in Scotland for independence. Some believe Nicola Sturgeon lacks the resolve to force a constitutional crisis into the open. She's too cautious; not a revolutionary. But she could soon find herself at the head of a movement for Scottish independence, which demands that she, and Scotland, start to live dangerously.