I have just been listening to Simon Heffer discussing the Powell and Pressburger film. All he says about the movie, which he admires, is true, but he does not give credit to the original novel by Nigel Balchin. Pressburger's script follows the novel fairly faithfully, certainly in terms of the main characters, though I dimly recall the conclusion to the novel as being more ambiguous than the film-makers' upbeat ending. The typical Archers' quirky touches do not detract from the central character study, and the visuals are great.
The one objection I have is in the climactic scene on Chesil Beach where Sammy Rice, coming off a massive bender, is attempting to defuse a deadly new German explosive device. In those days before speaker-phones, Rice gives a running telephone commentary on his actions to a young ATS corporal, who relays it to the brass in their hut at a safe distance from the site of the device. The tension builds as the camera moves in on the face of Renée Asherson, playing the ATS corporal.- then to my mind, dissipates as there is a cut to Rice and the bomb.
As Rice, this was David Farrar's finest performance. Sadly, his career went downhill from then on, as he tried to make it in Hollywood and, apart from a few supporting roles, failed.