Claire Ferguson’s documentary is a powerful, valuable addition to the Holocaust testimony genre, established 30 years ago by Claude Lanzmann. The film’s witnesses are now in their 90s, but in many cases extremely unfrail, almost as if kept in a kind of pain-racked vigour and electrified by the agony of memory, and by their determination to survive, to bear witness, to enforce a personal triumph over the forces of evil.

Llion Roberts, the film’s producer, interviews many survivors and each has a quietly devastating story to tell. Perhaps the most striking is the Pole Ed Mosberg, who was sent to the Kraków-Płaszów and Mauthausen camps, and who today gives lectures there in replica camp uniform. He is a taut, fierce, wiry figure, someone for whom the past is, in Faulkner’s words, not dead and not even the past. Much of the film is about the Kraków camp and the horrendous figure of the camp commandant Amon Göth, some of whose inmates were famously liberated by the factory owner Oskar Schindler; Ferguson does not allude to the Thomas Keneally novel or the resulting Spielberg film, and it is probably a wise choice to keep the focus simply on the historical facts.

For me, the most quietly devastating moment comes when Mosberg’s wife, Cesia, is shown simply looking at photographs of her relatives who perished in the camps and wondering how it was that she came to survive and others didn’t.