You thought it couldn’t get worse? It certainly can. Britain now faces the very real prospect of Boris Johnson moving into N0 10 (with or without his current girlfriend). He would do so as the country faces its gravest crisis since the Second World War – a crisis of which he was a principal architect – and without having won a general election. He would have been chosen, quite preposterously, by fewer than 120,000 ageing, reactionary Tory party members.

Rules are rules: the party with the most MPs selects the prime minister. But the Conservatives have no overwhelming popular mandate. Indeed, they were emphatically denied one in 2017. Theirs is a minority government sustained only by a squalid deal with the Democratic Unionist Party.

That tiny Tory franchise, utterly unrepresentative of the country as a whole, would impose on Britain the least qualified prime minister of modern times.

Johnson’s only ministerial experience consists of two dire years as foreign secretary – a stint memorable for his gaffes, gratuitous insults, guff about creating a “Global Britain” and constant undermining of Theresa May. As London’s mayor Johnson excelled as merrymaker-in-chief during the 2012 Olympic Games, but at little else: “Boris Bikes” were Ken Livingstone’s idea, the Thames cable car and ArcelorMittal Orbit tower were expensive flops, and his ultimate vanity project, the aborted Garden Bridge, cost £53m without a brick being laid. Before that, Johnson served briefly as shadow arts minister, but was fired by Michael Howard, then Tory leader, for lying about one of his extramarital affairs.

Johnson is also spectacularly lacking in the moral qualifications required to lead the country. He is a congenital liar, serially disloyal, untrustworthy, irresponsible and hopelessly chaotic – as David Cameron, Michael Gove, Nazanin Zaghari-Ratcliffe, his former wives, and many others know only too well. He may be a gifted and humorous wordsmith, but he deploys that talent to dupe, dissemble and deflect. He has shown an almost criminal disregard for Britain’s economic well-being (“Fuck business”) and for Northern Ireland’s fragile peace (he once compared its border to London’s congestion zone). He has no core principles beyond the advancement of one B Johnson, and the idea that he is motivated by a desire to help others is laughable. It is hard to recall a single act of Johnsonian selflessness.

This charlatan is now shamelessly cashing in on the national crisis that he helped bring about through his mendacious EU-bashing journalism and referendum campaign lies. He sells his views: £275,000 a year for a weekly Daily Telegraph column and five-figure sums for speeches.

Conservative MPs know all this. They have seen Johnson close up. Most loathe him. But they also know that he is adored by the party’s grass roots, and is the one leadership contender who can out-Farage Nigel Farage when it comes to demagoguery. With their seats at stake they are quite capable of compounding the nation’s woes by putting him on the shortlist of two to present to the party’s members.

It would be a desperate gamble. Johnson is no longer the amiable joker who twice defeated Ken Livingstone in Labour-leaning London. His support for Brexit has transformed him into Britain’s most divisive politician, save possibly for Farage. A recent YouGov poll showed 28 per cent of the public thought he would make a good prime minister – higher than any of his lacklustre rivals for May’s mantle. But a striking 54 per cent thought he would make a bad one – again way higher than his rivals. Even his siblings oppose him on Brexit. Johnson might staunch Tory defections to the Brexit Party, but he would also repel millions of moderate Tories and centrist voters. Nor is it easy to see how Johnson could negotiate a better Brexit deal than Theresa May. “We have blinked. We have baulked. We have bottled it completely,” he complains of the government’s efforts since 2016. We need to be tougher, he insists. To threaten a no-deal Brexit and to mean it. To force Brussels to blink first.

That is pure fantasy. Johnson is abhorred throughout the EU, which he once compared to the Third Reich. Europe’s leaders would know, moreover, that parliament remained overwhelmingly opposed to a no-deal Brexit. There is no way they would make concessions to Johnson that they denied to May. It is doubtful they would even agree to reopen negotiations, let alone extend the Article 50 deadline once more. At that point prime minister Johnson would have two options unless he, too, “bottled it” by opting for some form of soft Brexit.

He could call a general election which his deeply fractured party might well lose (could the likes of Ruth Davidson really campaign alongside him?). That would make him one of the shortest-serving prime ministers in history, and defeat would almost certainly mean the end of Brexit. Alternatively, Britain could crash out of the EU without a deal, the will of parliament notwithstanding. But the Tories would then own the immense damage to Britain’s economy and global standing that would ensue. Far from saving the Conservative Party, Johnson might be the leader who finally destroyed it.

Johnson’s fundamental problem is that the have-your-cake-and-eat-it Brexit that he promised voters in the referendum was never remotely attainable. If, heaven forbid, he becomes prime minister he will finally be exposed for the snake-oil salesman that he is, but the country will have paid a grievous price. Improbable as it seems, we might even feel nostalgia for Mrs May. For all her many faults, she is at least a grown-up.

Martin Fletcher is a New Statesman contributing writer and a former foreign editor of the Times