Code Breakers: Bletchley Park's Lost Heroes

Keeley Hawes narrates the story of how a 24-year-old maths student and a GPO engineer unravelled the secrets of Adolf Hitler's personal code machine - reputedly even more secure than the notorious Enigma device. The duo's work played an important role in ending the conflict in Europe, but because of its classified nature and continued application during the Cold War, the two men were never officially recognised.