The twin resignations of David Davis and Boris Johnson are the first time in more than 35 years that two UK Cabinet ministers have walked out within the same 24 hours. The last time it happened, the UK was grappling with the Falklands crisis.
That fact alone is a measure of how serious the situation facing the Prime Minister now is.
But the truth is, Monday’s events were always on the cards – it was just a question of when, and which of the Brexiteers would finally break ranks.
That it happened within not much more than 48 hours of the Chequers summit, which was finally supposed to have brought unity to a warring cabinet, shows how perilous the position is for Theresa May.
Before examining what this means for Brexit, it is worth recounting the fact that we are now more than two years on from the referendum result, but the UK Government has still not published the white paper outlining what it actually wants in leaving the EU. That will finally emerge later this week, unless more unforeseen events delay it further still.
But that two-year delay in spelling out any kind of coherent position is simply inexcusable. The truth is that Brexit has always been more about the internal politics of the Tory party than it has been about the national interest.
First of all, it was about the Conservatives’ attempt to see off the supposed threat from UKIP, and then, since the referendum, it has been about the ongoing battle of ideological purity within Tory ranks, as many of their MPs have sought to outbid each other in who can call for the most extreme Brexit possible.
The last two years have been, in some ways, the culmination, or at least the latest and perhaps defining chapter, of a 40-year civil war within the Conservative party.
But that internal obsession, in putting party interest ahead of the national interest, is a simply unforgiveable abdication of responsibility for any government.
The irony is that, for all the talk of Brexit being betrayed, the UK Government is still determined to take the UK as a whole out of the EU, the single market and the customs union. Scotland, of course, voted for none of these things.
I believe the Chequers plan is a step forward in that it appears to offer more realism than we have heard from the UK Government to date, although that may not be saying much. And, of course, we still do not know whether or not as a package it would be acceptable to the EU, in that it still appears to be cherry picking, trying to divide the four freedoms which are the cornerstones of the single market.
It is also horrendously complicated and, of course, it excludes provision for services, which account for almost 80 per cent of the Scottish economy, and a similar proportion of the UK economy as a whole. Around a third of our exports are services exports, so while the plan is a step forward from where Theresa May and her Cabinet were a couple of weeks ago, it is nowhere near good enough to protect all our vital economic interests.
An extreme Brexit, of the kind threatened by the Tories, also poses a direct threat to Scotland’s long-term economic well-being for many decades to come in the shape of the risk it poses to our working-age population.
That threat is one that hangs over the whole of the UK, but the differing demographics of Scotland mean that it is more true of the Scottish economy. Immigration is a subject that may be difficult for politicians to talk about, but it is one that we have a duty to be honest with people about, because the simple fact is that we need to continue to attract the best and the brightest talent from elsewhere. That is an economic imperative for Scotland, but is something that is directly threatened by Brexit.
Some commentators have speculated that the events of recent days have raised the prospects of a no-deal Brexit, whereby the UK crashes out of the EU next March with no agreement at all to take its place.
However, looking at the arithmetic in the House of Commons, I do not believe there is a parliamentary majority for a no-deal outcome. And I also think that after the Davis and Johnson resignations it is highly questionable whether there is a majority for the Chequers plan as it stands.
In my view, the only thing that actually stands a realistic chance of commanding a majority in the House of Commons, as well as being the right thing for the interests of the economy, is continued membership of the single market and customs union.
I have been consistent in saying that I do not want to leave the EU, in line with what people in Scotland voted for, but if the UK is to leave then the least worst outcome is one that keeps us in a single market which is around eight times bigger than the UK market alone.
That is supported by practically all mainstream economic analysis. And it is significant that in recent days we have started to see more and more businesses speak out about the very real threat which Brexit poses to jobs, investment and living standards right across the UK.
There is now a chance, I believe, that the events of this week will help pave the way for the least damaging Brexit. That was not the intention of David Davis or Boris Johnson in resigning, but it may yet be their legacy.