As Boris Johnson walked up to the podium at 10 Downing Street to make his first address as prime minister, they should have played Leonard Cohen’s Everybody Knows as his fanfare: “Everybody knows that the boat is leaking / Everybody knows that the captain lied.” For the one thing that can be said in Johnson’s defence is that he is not a conman. Yes, of course, he speaks fluent falsehood as his native language. But he deceives no one. Everybody knows.

The Tory MPs who backed him, the party members who voted for him so overwhelmingly, the media cheerleaders who hail his accession – they all know exactly what he’s like. They don’t believe him – they just wilfully suspend their disbelief. They cannot say they were taken in by a plausible charlatan – they choose to applaud the obviously implausible, to crown the man they know to be the Great Pretender. They go along with the fiction that Johnson is a Prince Hal who will metamorphose into the hero to lead England to a new Agincourt, while knowing damn well that he will always be a Falstaff for whom honour is just “a word”.

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Here is the most extraordinary aspect of this weird succession. All governments may end in failure but they are supposed at least to begin with some kind of gravity and some element of faith. As long ago as 1997, Johnson wrote: “Politics is a constant repetition, in cycles of varying length, of one of the oldest myths in human culture, of how we make kings for our societies, and how after a while we kill them to achieve a kind of rebirth.”

But King Boris starts out with no clothes. There are no vestiges of solemn dignity to drape the nakedness of his mendacity and fecklessness. The usual arc of a premiership runs from illusion to disillusion, from great expectations to more or less bitter disappointments. Even Theresa May, let us remember, seemed, at this same moment in the cycle in 2016, sincere and serious and deserving of some goodwill. The disillusion took a little while to set in. Johnson cannot disillusion anyone, for no one is under any illusion that he is truthful or trustworthy, honourable or earnest. His fitness for the highest office is not about to be tested – it is the most conspicuous absence in modern British political history.

The knowingness is all. Johnson’s genius has always lain in his ability to create a self-conscious collusion: complicity with the fiction known as Boris. He doesn’t have to have any character because he is a character. He is very good at making stuff up because he started with the biggest invention of all: himself. Sonia Purnell, in her excellent biography Just Boris, describes his careful disarrangement of his hair before TV appearances: “His famous dishevelled look is actually, however, the product of a brisk, artful rearrangement with his fingers (just before the cameras roll) rather than any naturally occurring disorder.”

And Johnson’s rise to No 10 is not a naturally occurring disorder either. It is the product of three decades of performances of the show called Boris Being Boris, an artful rearrangement of the standards of truthfulness and competence to which those who aspired to a public life had to at least pretend. His master at Eton, Martin Hammond, reported of him in 1982 that he regarded himself as being “free of the network of obligation which binds everyone else”. And his public career in journalism, showbusiness and politics has been all about preparing the notion that he should indeed be free, not just of the network of obligation, but of the ties to honesty and dignity that (however tenuous they become over time) politicians profess to be bound by.

Play Video 11:29 In full: Boris Johnson's first speech as prime minister – video

Johnson’s fictions have always had a kind of postmodern quality – everybody knows they are fictions. Take the example that Johnson himself has constantly cited, what he called his “foam-flecked hymns of hate to the latest Euro-infamy: the ban on the prawn cocktail flavour crisp”. Everybody knows and has always known that there was no such ban. Why? Because everybody could walk into a shop and buy a packet of prawn cocktail flavour crisps.

Equally, his more recent brandishing of a kipper to embody another Euro-infamy was a kind of camp self-parody in which the performance is everything and the relationship to truth simply irrelevant. In this sense, there is no more deception than there is at a pantomime. The point is not to make a claim about reality. It is to draw the audience into a knowingly comic complicity with unreality, so that, when the EU says “but we never banned prawn cocktail flavour crisps”, everyone can shout out together, “Oh yes you did!”

This has one enormous political advantage and Johnson has exploited it so superbly that he is now prime minister: he could never be found out because his mendacity was never hidden. Just three months before the Brexit referendum, Johnson was publicly and forensically exposed as a liar by his own party colleague Andrew Tyrie, who cross-examined him before the House of Commons Treasury committee and showed his claims about various EU regulations to be grossly distorted. In a courtroom drama, Johnson would have been led away in tears and handcuffs. But the hearing was not even a minor media story. Why? Because “Boris lies” is like Jonathan Swift’s “Celia shits”. Have I got news for you? No. Everybody knows already.

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It works because, with Brexit, a lot of people want to be lied to (it’s all going to be fabulous; the EU will shred the withdrawal agreement; the Irish will panic and do as they’re told). And if that is your desire, Johnson has another Leonard Cohen number for you: I’m Your Man. But – and this is the fundamental problem of his accession to power – a lot of people don’t want to be lied to.

Insofar as he has a strategy, Johnson’s plan is all based on the power of a lie, or to use the polite term, a bluff. The bluff is a no-deal Brexit. The basic belief of Johnson and those around him is that the way to get a great deal out of the EU is to pretend that you are quite happy to crash out without one. But bluffing only works if you do not already have a reputation as one of the world’s biggest bluffers. In this poker game, Johnson doesn’t have a tell. He is the tell. To put him into No 10 is to erect a neon sign over Downing Street that says: “Don’t believe a word of it.” The knowingness that Johnson has exploited to such great effect works within a circle of collusion. Outside the circle, knowingness is just plain old knowledge. Everybody knows that Johnson is the lying captain of a very leaky boat. Nobody in Europe is about to climb aboard.

• Fintan O’Toole is an Irish Times columnist and author of Heroic Failure: Brexit and the Politics of Pain