Some years ago the eminent political journalist and historian Peter Hennessy put forward the theory that the unwritten British constitution depended on what he called “good chaps” – that is, politicians and civil servants who kept the show on the road by understanding and respecting the unspoken assumptions on which political life depended for its smooth functioning. In the absence of clear rules about what constituted good behaviour and what didn’t, people in positions of power could be relied on to behave ethically and responsibly. Provided they did so the constitution would remain intact, and parliamentary democracy would continue to guarantee the fundamental rights of its citizens under the law.

As Hennessy reminds us in his latest book, Land of Shame and Glory – a political chronicle of a dramatic twelve months that began in August 2021 and ended in September 2022 – virtually every tenet of the “good chaps” philosophy came under severe strain, as the “good chaps” seemed largely to have left the stage. Above all, it was the prime minister, Boris Johnson, who violated virtually every unwritten principle on which British political life depended. Hennessy quotes the “Bagehot” column in the Economist from February 5, 2022, which regretted that Britain “still relies on shame to function … An absence of legal constraints requires an abundance of personal restraint, and Mr Johnson has none. A bad chap can go a long way”.

Johnson’s casual arrogance and supercilious irresponsibility have been known to those familiar with his character for a long time. When he was seventeen his house master at Eton, Martin Hammond, wrote to Johnson’s father, Stanley, complaining: “I think he honestly believes that it is churlish of us not to regard him as an exception, one who should be free of the network of obligation that binds everyone else”. Johnson, wrote Hammond, had adopted a “disgracefully cavalier attitude” to his studies, and seemed “affronted when criticised for what amounts to a gross failure of responsibility”. Nothing had apparently changed in Johnson’s character by the time he reached his mid-fifties.

Hugely popular with the Tory rank and file in the constituencies, thanks to his way with words, his humour, his shambolic appearance and his defiance of the often pompous and solemn way in which we are governed, Johnson owed his political success to the fact that the Conservative Party’s rules in the twenty-first century give the...