Writer Anthony Horowitz based the story of embezzlement at a wartime shipyard on an actual case of a Liverpool Shipyard owner who shot himself in January 1942. The Leftist convention alluded to actually did take place on January 12, 1941.
Dugald Bruce-Lockhart, who plays the Bomb Disposal commander, comes from a very appropriate background. His father and grandfather were both agents for MI6, his grandfather being in charge of SIS (MI6) in Germany for some years after the war. His great-great-uncle, Sir Robert Bruce Lockhart, during the Second World War was Director-General of the Political Warfare Executive.
Parts of this episode were filmed at the Chatham Historic Dockyard, using two museum ships as a backdrop, the submarine HMS Ocelot in the dry dock, and the destroyer HMS Cavalier tied up to the pier.