It wasn’t the failure to deliver Brexit that did for Theresa May.  It was something even bigger: breaking her word.  She pledged over a hundred times that Britain would leave the EU on March 29, and it didn’t.  She then said that she was not prepared to delay Brexit later than the end of June, but did.  She declared that it would be “unacceptable” for European elections to take place, but they happened.  She denounced Jeremy Corbyn as a threat to the country, but then sough to deliver the Withdrawal Agreement by making a deal with him.

The most elemental trope about politicians, as Lord Ashcroft’s latest focus groups confirm, is that they are all liars.  So it came about that May dragged the Conservatives down to nine per cent and four MEPs in those Euro-elections.  Tory poll ratings slumped to 20 per cent.

It is Boris Johnson’s promises to take Britain out of the EU by October 31, “do or die”, that has dragged the Conservatives up the polls by their bootstraps.  If he backtracks on it, there can be no doubt that, once again, the Tory ratings will slide into the abyss, and drag him down with them.

By the time the Party crawls out, it would not only find a Marxist Labour Party in its place as the government but, in all likelihood, that the Brexit Party has supplanted it as the county’s main right-of-centre electoral force.  And the Conservative Party’s century-and-a-half run as the most enduring governing party in the world would end.

So it comes about this morning that the Prime Minister writhes amidst the grandmother of all pincer movements.  One the one hand, he cannot implement an extension.  On the other, he cannot (or rather, must not) break the law.  He must choose between the unspeakable and the unthinkable.

Now it may be that he can somehow slip out of the pinch.  Some ingenious means of doing so are being floated.  One is use of the Civil Contingencies Act.  The latest is that Johnson send a letter with the letter of extension contradicting the letter of extension.  Some are reduced to hoping that an EU state simply deploys a veto.

One suggestion put to this site by a reader, apparently in all seriousness, is that he send the letter by carrier pigeon, so that it arrives after the deadline.  It may be that the Prime Minister and Dominic Cummings have a plan that will really fly.  But when matters reach this pass, you know that the game is up.

A Cabinet Minister this morning is reported quoting Sherlock Holmes: “how often have I said to you that when you have eliminated the impossible, whatever remains, however improbable, must be the truth?”  Quite so, though not perhaps in the context that the Minister intended.

If Johnson cannot deliver Brexit by October 31, and is barred from doing so by law, there is only one practicable course left open to him: to resign as Prime Minister.  “I won’t break the law,” he must tell the British people.  “But I won’t break my word either.  If Corbyn wants to sign this surrender document, so be it: I won’t.”

Johnson’s hope would be that the Labour leader requests and obtains an extension; that the Commons keeps him in place only for as long as it takes Corbyn to do so; and that it then brings him down in a no confidence vote, paving the way for an election in which Johnson marginalises the Brexit Party and sweeps the board.

There are problems with this course.  The first is that the plan might not work at all.  The anti-No Deal majority in the Commons might of course not let Corbyn become Prime Minister – even briefly, to request and obtain an extension.  It might settle on someone else instead (Ken Clarke?), with unforeseeable consequences.

The second is that it might work too well.  Corbyn indeed becomes Prime Minister, requests an extension and get it.  But the anti-No Deal majority in the Commons, fearing a Johnson victory at the polls, does not then no confidence Corbyn.  Instead, it props him up and keeps him in place, at least for the time being.

And as the weeks drag on, Johnson himself is subjected to a leadership challenge – in which the voluntary party, which backs him, would have no say.  It might well not be successful.  But even so, the consequences for the Party are necessarily unknowable.

It will also be asked: what’s the point of seeking to avoid a Corbyn Government by trying to put in a Corbyn Government?  The question is a good one.  But as so often in politics, we must find the least bad answer rather than search for the perfect one, which doesn’t exist in any case.

The choice may come down to the possibility of Johnson resigning as Prime Minister, Corbyn succeeding him briefly to agree an extension, and Johnson then sweeping a general election…or the certainty of Johnson, were he to agree an extension, consigning himself to the disposal dump of history, and perhaps the Conservative Party too.  Some will say that instead of disdaining the Brexit Party as a competitor, the Tories should embrace it as a colleague instead, and merge the two into an electoral alliance.

We will probe the matter later this week.  But one thing’s for sure: such a pact would have no bearing on the choice that now Johnson seems to face: request an extension, and you destroy yourself (and perhaps your Party too).  Don’t request it, and you break the law (and it doubtless happens anyway).   If there is an escape from this trap other than resignation, we would love to know what it is.