The greatest film of all time? Until the next Sight and Sound critics’ poll, due in 2022, the official title holder is Alfred Hitchcock’s Vertigo. Every ten years since 1952, that august journal has polled the world’s leading film commentators on their top movie. In the results for 2012, Hitchcock’s strange and luscious film (about a man obsessed by a woman who seems to have returned from the dead) finally put an end to fifty years of triumph for Citizen Kane by Orson Welles. Shrewd observers had seen this coup slowly coming over the previous three decades. In 1982, Vertigo – a critical and commercial flop on first release – came sneaking into the list out of nowhere (it was not even available for public screening at the time) to take seventh place. By 1992 it had crept up to fourth place, and by 2002 to second. Hitchcock’s posthumous star rose as Welles’s waned; in the end, the fat chap from Leytonstone trounced the obese guy from Kenosha.

How and why did this happen? Or, to ask a question that seldom crops up in Hitchcock’s thrillers, who done it? (We know, pretty much, that Norman Bates done it in Psycho and that the Nietzschean thrill-killers done it in Rope, just as we know that Robert Donat didn’t do