Keeping a mistress was essential to John le Carré’s success

Adam Sisman is sensitive to the charge that a book about an author’s unknown mistresses is simply an exercise in prurience. ‘I am not one of those who believes sex explains everything,’ he declares defensively.

But this admirably concise volume justifies its title. Sub-themes such as the practice and ethics of biography, and the emotional toll taken by spying, run through it. But its core relates how, when writing his 2015 life of David Cornwell (John le Carré’s real name.) Sisman was prevailed upon to delete details of his subject’s many extramarital affairs. In fraught pre-publication negotiations, he met Cornwell’s son Stephen, who suggested he keep this material as a ‘secret annexe’ to appear later.

This is that ‘annexe’ (everything seems to require the adjective ‘secret’). Sisman argues plausibly that Cornwell’s career in intelligence was uneventful, and well covered in his biography. Cornwell made it sound more mysterious than it was. Any idea that he was marked out to be head of SIS is rubbish.

But he used his experiences to carve a career as a hugely successful author of spy novels, and Sisman believes his self-confessed ‘messy’ love life is the key to unlocking his fiction. Cornwell himself told him that his infidelities ‘produced in my life a duality and tension that became almost a necessary drug for my writing’. Sisman concedes that they energised his world, acting as a substitute for espionage, and giving relief from the tedium of the writer’s solitary life.

Sisman traces the story back to Cornwell’s mother, not, as often mooted, his father. She deserted him at a young age and left him with a lifelong distrust of women.