“My instructions were to film everything which would prove one day that this actually happened.” Producer Sidney Bernstein’s 1945 documentary German Concentration Camps Factual Survey (on which Hitchcock played a key creative role) remained unfinished until a recent Imperial War Museums reconstruction, which will screen at the London film festival next month.

This impressively sober, thoughtful documentary serves as a contextualising companion piece, juxtaposing horrifying raw footage with interviews with those who first viewed these appalling, devastating images. Editor John Krish recalls watching four hours of Dachau footage in negative; US sergeant Benjamin Ferencz says: “I had peered into hell.” Crucially, director André Singer also investigates the original suppression of Bernstein’s film, which became “a political inconvenience”.