Continuity mistake: It is 1940. Two pilots come out of a house - one of them has just lost his wife and family in the London Blitz, the other is an RAF Squadron Leader. The door they come out of has a modern electric bell push - a post 1965 version, white rectangular box with a round button.
Trivia: During the scenes dealing with the dive bomber attacks on the RAF radar stations, the filmmakers used rather un-convincing radio-controlled models to portray the German Ju87 Stukas. Originally, the producers had intended to use Proctor trainers, modified to resemble the Stuka. However the British aviation authorities refused to pass them as airworthy, forcing the producers to resort to using the models.