Jo Johnson’s resignation may not have much practical effect, but it is symbolic, and it dramatises his brother’s problem.

The prime minister cannot have an early election, because Labour MPs refuse to vote for it. He won’t ask for a Brexit extension, as required to do by the backbench bill that will be law by Monday. It looks as if he will have to resign.

Boris Johnson could even announce his intention to resign – as prime minister but not as leader of the Conservative Party – on Monday. He would have to do it anyway by 19 October, which is the date set in Hilary Benn’s bill by which whoever is prime minister would have to sign a letter to Donald Tusk, the EU president, asking for an extension to the Article 50 period.

But what is the point of waiting? Once Benn’s bill becomes law on Monday, the prime minister is trapped. As he said in the Commons yesterday, “It is a bill that effectively ends the negotiations.” There is not much more for him to talk about with the EU, because the other EU leaders know that we won’t be leaving without a deal on 31 October.

Johnson could spend the next five weeks just being prime minister, without parliament to bother him, but on borrowed time. He could attend the EU summit on 17-18 October, but with nothing substantive to say.

Whenever he chooses to announce his resignation, his only alternative would seem to be to eat not just his words but his pride and any semblance of credibility with Leave voters.

Biggest lies told by Boris Johnson Show all 5 1 /5 Biggest lies told by Boris Johnson Biggest lies told by Boris Johnson Made-up quote for The Times Johnson was sacked from The Times newspaper in the late 1980s after he fabricated a quote from his godfather, the historian Colin Lucas, for a front-page article about the discovery of Edward II’s Rose Palace. “The trouble was that somewhere in my copy I managed to attribute to Colin the view that Edward II and Piers Gaveston would have been cavorting together in the Rose Palace,” he claimed. Alas, Gaveston was executed 13 years before the palace was built. “It was very nasty,” Mr Johnson added, before attempting to downplay it as nothing more than a schoolboy blunder. PA Biggest lies told by Boris Johnson Sacked from cabinet over cheating lie Michael Howard gave Boris Johnson two new jobs after becoming leader of the Conservatives in 2003 – party vice-chairman and shadow arts minister. He was sacked from both positions in November 2004 after assuring Mr Howard that tabloid reports of his affair with Spectator columnist Petronella Wyatt were false and an “inverted pyramid of piffle”. When the story was found to be true, he refused to resign. PA Biggest lies told by Boris Johnson Broken promise to boss In 1999 Johnson was offered editorship of The Spectator by owner Conrad Black on the condition that he would not stand as an MP while in the post. In 2001 he stood - and was elected - MP for Henley, though Black did allow him to continue as editor despite calling "ineffably duplicitous" PA Biggest lies told by Boris Johnson Misrepresenting the people of Liverpool As editor of The Spectator, he was forced to apologise for an article in the magazine which blamed drunken Liverpool fans for the 1989 Hillsborough disaster and suggested that the people of the city were wallowing in their victim status. “Anyone, journalist or politician, should say sorry to the people of Liverpool – as I do – for misrepresenting what happened at Hillsborough,” he said. PA Biggest lies told by Boris Johnson ‘I didn’t say anything about Turkey’ Johnson claimed in January, that he did not mention Turkey during the EU referendum campaign. In fact, he co-signed a letter stating that “the only way to avoid having common borders with Turkey is to vote Leave and take back control”. The Vote Leave campaign also produced a poster reading: “Turkey (population 76 million) is joining the EU”

He could, I suppose, ask for a Brexit extension and say he wants another referendum, which could take six months and leave him a broken leader in the meantime. But I would have thought he’d rather say that he wants an election; that parliament has blocked him; that he will leave it to others to sort out the constitutional deadlock; and that he will fight the election when it comes.

To many people, he will have failed, because Brexit will have been delayed again – but at least not by him. He could say that he tried, but the people were betrayed by a Remainer parliament that never accepted the result of the 2016 referendum. The Brexit Party would be stronger than it would have been in a 15 October election, because Nigel Farage will accuse Johnson of breaking his promise to get us out “come what may” on 31 October. But Johnson would still have a chance of fighting a “people versus parliament” election against a divided Labour Party.

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No one knows what would happen if Johnson announced his resignation. He would, presumably, refuse to advise the Queen as to whom she should invite to form a government instead. We would be in the unlikely territory of the House of Commons having to try to unite behind someone as temporary prime minister.

This caretaker figure would be charged with writing the “Dear Donald” letter that Johnson refuses to write, and then presiding over an election – after 31 October.

But who could it be? Jo Swinson, leader of the Liberal Democrats (now 16 strong), doesn’t want Jeremy Corbyn; and it’s hard to see Corbyn acquiescing to Kenneth Clarke, now an independent Conservative. I have argued before that Clarke has more implied support in the Commons than Corbyn has.