Here is the measure of the madness.

An influential Cabinet minister Amber Rudd has resigned in a blaze of recriminations, citing the “assault on democracy and decency” of Johnson’s expulsion last week of 21 Tories who oppose a no-deal Brexit.

But it will change nothing.

A lamed government without a majority won’t fall because the opposition does not want it to fall yet - not till after the EU summit of 17-18 October, such that their new law, that seeks to delay Brexit, has a chance to work its magic or its evil (up to you whether you think it’s white or black).

Rudd has been replaced at Work and Pensions by Therese Coffey, a personable minister apparently less frightened by a no-deal withdrawal from the EU. And there was seemingly no shortage of candidates for two months of being driven in an official car and bring called Right Hon. “Lots of ambitious younger types already texting” a Downing Street source told me last night.

But there is no chance of the new pensions secretary doing anything that might require a vote of MPs, because Johnson as a matter of policy (with his expulsions) has put a triple lock on his inability to govern.

Therese Coffey is apparently less frightened by a no-deal withdrawal from the EU. Credit: PA

Ne’er mind eh. There won’t actually be any votes for an unprecedented five weeks after the House rises on Monday night or Tuesday.

Johnson will then have five weeks, relatively unchallenged, to set out his stall for the general election, that will probably come in November, and also to prepare himself for the final test of whether direct democracy - the EU referendum in this case - trumps or is trumped by parliamentary democracy.

That test would terrify most prime ministers, because - as I’ve been saying - it involves him breaking the new law that would require him to sue EU leaders to delay Brexit till 31 January.

I’ve said it before and I will say it again, the notion of a prime minister - especially a Tory one - breaking the law is extraordinary.

But Johnson - and his aides led by Dominic Cummings - feel they have no choice.

Because if Johnson fails to be seen to sacrificing himself for the 17.4m people who voted for Brexit, Johnson believes (probably rightly) that his time as PM will be up forever, the Tory Party will be destroyed by Farage’s Brexit Party and Brexit will be lost.

Amber Rudd's resignation may not matter in the grand scheme of things. Credit: PA

For Johnson, the logic of being held in contempt for disobeying the law, of the Supreme Court ultimately determining whether Brexit is delayed and who governs, is impeccable.

But this is to put a bomb under the unwritten constitution of the UK. Nothing like this has ever happened in our parliamentary democracy.

If Johnson were to continue to insist he would not ask for a Brexit delay, even at pain of imprisonment, what then?

Whether or not it actually happens, the idea that a PM might knowingly risk imprisonment by defying MPs is not what you expect in John Bright’s mother of parliaments. It would turn the UK into an even greater freak of the democratic western world than we appear right now. So much the worse.

The point for Johnson is that if he were to lose a no-confidence vote after the EU summit and after he refused on or after 19 October to sign the pro-forma Brexit delay letter, there probably isn’t enough time to replace him with a caretaker PM or trigger an election BEFORE Brexit day on 31 October. So the UK would be out of the EU, at the modest price of total constitutional collapse.

It is all part of Johnson’s message to 27 EU leaders, “read my lips, we are leaving the EU on 31 October, deal or no deal”.

Boris Johnson could have five weeks, relatively unchallenged, to set out his stall for the general election. Credit: PA

Believe it or not - and Rudd says she does not - Johnson and Cummings see signs of movement towards a backstop compromise and therefore a possible Brexit deal.

That putative progress is mostly around the supposedly softening opposition of Northern Ireland’s DUP - Johnson’s vital unionist allies - to allowing the whole island of Ireland to remain governed by EU standards for agriculture and food, with an agricultural and food-standards border between Northern Ireland and Britain in the Irish Sea. It is about compromise by Johnson that might just tempt Dublin into constructive negotiations.

But it is ludicrously premature to see here a compelling plan to salvage an orderly Brexit from the jaws of chaos.

What it is however is proof that even if Johnson secures a Brexit deal, it will almost certainly be loathed as yet another surrender to Brussels by the Tory party’s ERG Brexit purists, such as Francois and Baker (who will also notice soon enough that there is little attempt by Johnson to change the other elements they loathe in May’s Withdrawal Agreement).

At which point, if they were to vote against any Brexit deal Johnson miraculously puts to parliament, they like the 21 Tory remainers would be expelled. And there might well at that juncture be only a handful more official Tories in parliament than Labour MPs.

This is politics like Hayek’s approach to banking in the 1930s, which was that the only way to save banking and the economy was to let the banks collapse.

Will the Conservative Party, and parliamentary democracy, be saved or sunk by Johnson’s evisceration of the Tories?

We’ll find out soon enough. This is not a drill.

Robert Buckland could become the next Cabinet departure. Credit: PA

Update 10.55am

There is much talk Robert Buckland will resign from Cabinet on Sunday because as Lord Chancellor he could not stay knowing that Boris Johnson plans to break the Brexit-delay law.

Also much of the Cabinet, Culture Secretary Nicky Morgan et al, will quit if Johnson breaks the law on October 19.

Yup, we are close to Defcon 1.

Update 11.50am

The Lord Chancellor Robert Buckland is staying put and will not resign unless and until Boris Johnson breaks the law, I understand. Buckland has told the PM that honouring the rule of law is the defining issue for him.

So the big moment for Buckland - and for the attorney general Cox and for half the cabinet - will come on 19 October, when Johnson will have to decide whether to honour the law by signing the pro-forma letter asking for a Brexit delay or break it by refusing to sign.

For what it’s worth I am told Buckland asked the PM whether he intended to honour the Brexit delay law and Johnson replied “we are law makers not law breakers”.

We’ll see.