Because Boris Johnson has such a notoriously casual relationship with the truth, there is a tendency not to take him seriously, even on the occasions when he is probably speaking with an unforked tongue. So there has been a lot of derision for his declaration that he would “rather be dead in a ditch” than ask the EU for an extension to the Brexit deadline.

Seriously? Even if instructed to do so by the legislation that will be written into the statute book this week? Would he break the law, a ditch no previous occupant of his office has chosen to expire in? That, I think, is ultimately unlikely. He wouldn’t like the food in prison. So might he resign as prime minister rather than carry out parliament’s orders? Yes, I think he might do that. He would not want to quit. He may not have realised yet that the positions he has taken will compel him in that direction. But I think we may get to the point where resignation from Number 10, taking his government with him, ends up being his least worst option. He has been boxed by parliamentary votes that will not let him have a no-deal Brexit. He has been coxed by the opposition refusing him an election. The one thing they can’t stop him doing is quitting as prime minister and taunting the Commons to find someone else to carry out its instruction. Deposing himself may turn out to be the most powerful card left in his hand.

This was not in the original cunning plan when he arrived in Downing Street. The scheme did not envisage Mr Johnson having to hand in his cards to the Queen only weeks after becoming prime minister. If he ends up there, it will be the result of a series of miscalculations that have led to him losing control of Brexit, parliament and election timing in the space of less than a week.

The first hubristic error was to announce the prorogation of parliament. Instead of greasing the wheels towards a no-deal Brexit, this provoked appeals to the courts and demonstrations outside Buckingham Palace. Most importantly, it galvanised opponents in the Commons. He managed the remarkable feat of uniting the Labour party not only with itself, but with other opposition parties. Having spent much of the summer engaged in dismal squabbling about how best to thwart a no-deal Brexit, they rallied around the standard of defending parliamentary rights against a dictatorial executive. They then made common cause with each other and Tory rebels to legislate against a crash-out Brexit.

Making that vote a form of confidence issue was the next big misjudgment that backfired on the Johnson regime. Having made that nuclear threat, it had to be carried out, but the price has been huge. Stripping the 21 rebels of the Tory whip was the most brutal bloodletting in the party’s modern history. The casualties of the purge include no less than seven former cabinet ministers, among them Ken Clarke, who served in the Heath, Thatcher, Major and Cameron governments. As the Father of the House points out in our interview with him in today’s Observer, he first became an MP when Boris Johnson was “a small toddler”. Treating someone who has been a Conservative MP for nearly half a century as a traitor to Toryism shows just how far the party has become unanchored from its traditional principles. In anticipation that the Tory party will effectively run on a no-deal manifesto at the now looming election, a clutch of moderate Conservatives have since declared that they will not stand again, among them the prime minister’s younger brother, Jo. That was the most personally wounding blow of the prime minister’s catastrophe-strewn week.

Facebook Twitter Pinterest MP Ken Clarke was among the casualties of the most brutal bloodletting in the Conservative party’s modern history. Photograph: Toby Melville/Reuters

The worst miscalculation of the supposed grandmasters of political chess at Number 10 was to think they could then strike back by triggering an election on the prime minister’s terms. The Johnson crew were convinced that an election was an offer the opposition could never refuse. After all, Labour facilitated an early election for Theresa May in 2017 even though she had a whopping poll lead at the time of the parliamentary vote to allow it and most Labour MPs thought it was going to mean a Tory landslide. So you can see why Number 10 believed this ploy had to work, but it turns out that there are still some people in the Labour party who can think a few moves ahead. Along with the other opposition parties, they decided to deny Mr Johnson an election timed for his convenience. Thus we have entered the looking-glass world in which a prime minister who wants to gamble the job he has only just acquired on an election is kettled inside Number 10 by Jeremy Corbyn.

Tories hope, and some on Mr Corbyn’s frontbench are nervous, that Labour will pay a price for appearing “frit”. I am not sure about that. Past campaigns suggest that voters quickly forget how an election date came to be decided and concentrate instead on the choices before them.

So the parliamentary tactics have exploded in his face, but this does not mean that his overall strategy is going to change. He has deepened the divisions in the Tory party. His chances of securing a refettled deal from the EU, never exactly high in the first place, look vanishingly slight. His scheme to force a snap election has been stymied. But like Macbeth, he is too stepped in blood to turn back now. He will double down on trying to frame the election battle as a choice between “people and parliament”, even if that means the sacrifice of more of his party’s reputation with moderate voters.

Will the expulsion of so many Tory MPs push more swing voters over to the Lib Dems? Highly likely. Will the Conservatives’ electoral chances be diminished when the prime minister’s own brother so little trusts him that he has sacrificed his parliamentary career? History suggests that the Tories will suffer for that. Is the metastasis of the Tories into a version of the Brexit party going to cost them seats, especially in Scotland, London and the south? This is very probable too. But then these were always going to be consequences of his “do or die”, “whatever it takes”, “come what may”, “shit or bust” strategy. It is predicated on the assumption that his single most important task is to squeeze down the Brexit party – to “put Farage back in his box”, as he has said. Its overarching ambition is to recreate something resembling the coalition of voters that delivered the Leave outcome in the referendum in the hope that the British electoral system will translate that into a parliamentary majority for a hardcore Brexit.

The electoral gamble is that the seats lost by the Tories will be more than compensated for by taking seats from Labour in Brexity areas currently represented by Labour MPs. The events of the past week have not so much changed the trajectory of the Tory party as accelerated it along the path it chose to take when it made him its leader.

To have any chance of pulling off this massive gamble, he will have to retain credibility with pro-Brexit voters. Any hope of doing that would be shattered were he to go along to the EU and grovel, as Brexiters would see it, for another delay. Breaking the law would land him in the courts. Asking for an extension while protesting that he has been forced into it by parliament would look no better. In Brexiter eyes, that would turn him into a pathetic puppet prime minister. Though no one in the opposition parties is prepared to admit this in public, the boost this would give to the Brexit party at the expense of the Tories is one of the reasons the opposition wants to delay an election beyond the end of October.

Allies report that Mr Johnson has privately said that he would rather resign than be the prime minister who asked for another postponement of Brexit. I think I believe that. Either Jeremy Corbyn or someone from the so-called Rebel Alliance would then have to take over in order to ask for the extension – after which the temporary unity between them would likely start to crack. Boris Johnson would campaign as the leader of the opposition, a role in which he would be more comfortable anyway, asking for a Tory majority to deliver the Brexit that parliament had stopped. I know it sounds incredible, if not insane. And yet once you have eliminated the impossible, whatever remains, no matter how improbable, must be the truth. In so much as there is any logic left in British politics, it points towards Boris Johnson being impelled to depose himself.

• Andrew Rawnsley is Chief Political Commentator of the Observer