YOU KNOW HOW THIS BEGINS:We all think we know him: dressing gown; the cigarette holder; the utterly imitable voice, recognisable by even the very worst impression. It has become a cliché to note even in passing what a cliché the cliché has become, before polishing off the opening paragraph with the eternal Coward Question: “But what really lies behind the mask?”

Until now, biographers’ attempts at an answer have comprised, perforce, fantastical dollops of conjecture, their primary sources being invariably unreliable and sometimes entirely made up: Coward’s autobiographies (from diaries which, as his fame increased, were written with publication in mind — thoroughly expurgated and exaggerated); his contemporaries’ haute couture