The trivia item below may give away important plot points.
Filmed on location at Bawdsey Manor, Suffolk, where Robert Watson-Watt invented, and developed Radar immediately prior to the outbreak of world war 2. Filming also took place across the river Deben from Bawdsey, at Felixstowe Ferry. The muddy denouement was filmed on the foreshore, and in a specially created pit, as it was too dangerous to risk getting stuck in the mud where the fast flowing Deben enters the North Sea. The London dock scene, right at the beginning, is in fact, the ancient Saint Peter's dock in Ipswich, with Tower Bridge added as a digital composite.