Boris Johnson has been accused of many, many things over the years. But the parties and the lies, the sleaze and the juicier scandals don’t seem to interest historians Anthony Seldon and Raymond Newell much. Their central complaint in this utterly scathing account of his time at No 10 is the more fundamental one that, as they put it, he “never understood how to be prime minister, nor how to govern”; that he didn’t know what he was doing, barely bothered learning, and was so lacking in moral seriousness that even when he tried he couldn’t transcend the limitations of his “base self”. It’s a lofty charge, but a grave one nonetheless. A career headmaster and stickler for detail who has published report cards on each prime minister back to Tony Blair, Seldon was never likely to warm to the overgrown schoolboy Johnson, and so it proves. The story really begins with Johnson’s response to his side winning the Brexit referendum: far from celebrating, they write, he paced the house looking “ashen-faced and distraught”, panicking aloud that: “Oh shit, we’ve got no plan. We haven’t thought about it. I didn’t think it would happen.” What weighed most heavily in his choosing leave over remain, they suggest, was his own personal ambition. From this unfolds a tale of power pursued without much purpose, or latterly dignity. The authors do discern three vague political impulses in Johnson – a love of infrastructure projects, an aspiration to level up, and patriotism – but conclude these never cohered into policy. Lacking an agenda himself, Johnson was easily swayed by those who had one, notably Dominic Cummings (accused here of repeatedly overstepping the mark in pushing his own ideas as an unelected adviser) and later his chancellor Rishi Sunak. The book describes a prime minister alarmingly unable to focus and seemingly out of his depth, who Cummings felt should be kept out of Brexit negotiations because “he didn’t understand them”. He promoted mediocre ministers who didn’t threaten him, played rival aides off against each other, and showed shockingly little interest in major issues such as education; privately agnostic about the divisive “war on woke”, he nonetheless let his government wage it vigorously. Even those closest to him struggled to discern his real opinions. The case for Johnson’s defence is usually that he got Brexit done, rolled out a Covid vaccine and stood with Ukraine. But Seldon and Newell argue that Brexit hasn’t delivered as promised, that the real vaccine heroes were the chief scientific adviser Sir Patrick Vallance and NHS executive Dr Emily Lawson, with the European Commission president more influential on Ukraine. Johnson genuinely did want, they concede, to transform social care, having seen his own mother Charlotte struggle with Parkinson’s. But by the time he tackled it, he lacked the political capital for the fight. The book’s weakness is that its charges of chaotic vacuousness are not new, while the sheer flimsiness of Johnson’s programme provides such heavyweight authors with too little to get their teeth into; the overall effect is rather like sending distinguished theatre critics to cover a school nativity play. But this howl of scholarly frustration has three strengths. Firstly, it sets the scene for Sunak’s time at No 10, sketching an early outline of someone who lacks Johnson’s flaws but may also lack one of his few redeeming instincts, an impulse to spend money on public services when necessary. Secondly, it refutes the dangerous myth that Boris Johnson was foiled by a remainer establishment, rather than his own incompetence. His former chief of staff Eddie Lister declares that there is “no evidence that the civil service impeded the delivery of Brexit” and the authors conclude that if Johnson didn’t always get what he wanted from Whitehall, that’s because he led it poorly. And thirdly, it’s a timely reminder of how good government should work. When Downing Street is functioning well, the authors write, the machine becomes so highly attuned to the prime minister’s vision that it responds appropriately even when there’s no time to think. “In the most effective premierships, Number 10 becomes the prime minister. It becomes one mind.” It’s just the nation’s bad luck that for three years, it became Boris Johnson. Johnson at 10 is published by Atlantic (£25). To support the Guardian and Observer, order your copy at guardianbookshop.com. Delivery charges may apply.