Written once their authors have lost power, most prime ministerial memoirs try at some level to be reflective. David Cameron’s begins by confessing that he still has daily anxieties about having called the Brexit referendum. John Major’s starts even more disarmingly, by wondering why he went into politics at all.

But Boris Johnson does not do reflective. He never has and he never will. And nor does his new memoir, with its unnerving title, Unleashed. It covers his time as London mayor, Brexit campaigner, foreign secretary and prime minister. But if it is heart-searching and confessions you seek from the pen of Britain’s most iconoclastic prime minister, you can stop now.

This is not “the political memoir of the century” as the Daily Mail has been billing it for the past week. Or, if it is, an unrewarding 76 years lie ahead for the publishing industry. Take this passage from the section describing how Johnson felt in April 2020 when he had to be transferred from Downing Street to St Thomas’ hospital suffering from Covid:

It wasn’t just the physical distress; it was the guilt, the political embarrassment of it all. I needed to be bee-oing-oing back on my feet like an india rubber ball. I needed to be out there, leading the country from the front, sorting the PPE, fixing the care homes, driving the quest for a cure.

There’s a lot worth parsing there. And plenty that is characteristic of Johnson’s writing more generally. There’s the rubber ball image and the exuberant vocabulary. But then there’s also the sheer dishonesty and the lies. In reality, Johnson was a chronically indecisive prime minister, emphatically not one who led from the front. The PPE wasn’t being sorted at all, either, nor the care homes fixed. His solipsistic admission that he thought going into hospital was an embarrassing look for a leader shows where his instinctive priorities lay.

Then there are the political omissions. Johnson records Prof Chris Whitty, the chief medical officer for England, warning – rightly – at the outset of the pandemic that the public would expect the government to act, to make rules and to enforce them. Yet listen to the Covid inquiry, and the evidence of what things were really like at the heart of Johnson’s government in 2020 is jaw-dropping. “I’ve never seen a bunch of people less well equipped to run a country,” said the cabinet secretary, Simon Case, in a WhatsApp message.

Johnson’s book gives his version of the big episodes. But it dodges the larger issues they raise. The description of what he calls “the whole Partygate hoo-ha” is typical. It is full of angry self-righteousness. But his conclusion that he should not have apologised so much over Partygate is strikingly tin-eared. Though Johnson likes to parade the outward signs of his intellect, there is not a philosophical sentence in the entire book.

Yes, he often dresses up his memoir in amusingly image-rich and alliterative language. Donald Trump is “like an orange-hued dirigible exuberantly buoyed aloft by the inexhaustible Primus stove of his own ego”, for example. Kate Bingham did Covid vaccine deals “like a slightly tipsy billionaire at the Grand National”. Oliver Letwin is “the Professor Branestawm of British politics”.

And, yes, he regularly uses a cascade of words when a single one would do. “I wanted to create ladders, springboards, trampolines, catapults – anything to help kids with energy and talent,” he writes on his levelling up policy.

The freewheeling nature of the memoir is entertaining but becomes irritating for its lack of structure. You will search long and hard to find any other political memoirist who could reflect, after Cameron threatens to “fuck you up for ever” if Johnson opts to back leave in the Brexit campaign: “Did I want to be fucked up? For ever? By a prime minister equipped with all the fucking-up tools available to a modern government, and thousands of fucker-uppers just waiting to do his bidding?”

It is important to remember, though, that this has always been Johnson’s way. He uses his wit, appearance and persona to deflect from serious matters and to advance his own cause. His language is a form of collusion with his audience to stand apart from the tough business of governing. As Ed Docx observed in 2021 in these pages, Johnson has perfected the role of the clown king, whose speech is “not – in truth – eloquent, but rather the caricature of eloquence”. It is the same with this memoir.

That is not to deny that some of his anecdotes are striking. Johnson really does seem to have seriously contemplated a ludicrous armed raid on the Netherlands in order to bring millions of AstraZeneca vaccine doses to Britain. He did almost drown on holiday in Scotland in summer 2020 because he was determined to sit out at sea in an inflatable kayak to avoid the Highland midges. And he comes super-close to implying that Benjamin Netanyahu personally planted a listening device in his private departmental bathroom when Johnson was foreign secretary.

Just occasionally, there is an almost casually delivered shaft of self-knowledge. “I am afraid, looking back, that I allowed the wish to be the father to the thought,” he writes. He is talking about Northern Ireland policy at this point, but the insight applies to much else in Johnson’s career, including Brexit, levelling up and his ability to govern. It probably describes his chances of a return to power too.

Perhaps this overhyped book is the only memoir of which Johnson is capable. He is not going to change. Anyone wanting more about his time at the top will gain greater insight from a few pages of Anthony Seldon and Raymond Newell’s Johnson at 10 than they will from Unleashed’s more than 700 pages. Unleashed to do what? We never learn – and even he may not really know either.

• Unleashed by Boris Johnson will be published on 10 October by William Collins (£30). To support the Guardian and Observer, preorder your copy at guardianbookshop.com. Delivery charges may apply