Dozens of Whitehall lines and calls to large armament contractors were eavesdropped for signs of careless talk following a request from MI5 during World War 2.

But records released under the Freedom of Information Act also offer a portrait of wartime Britain straining under the pressure of the war effort and air raids.

As well as conversations about shipments and plans, the Postal and Telegraph Censorship Department of the Ministry of Information recorded tense conversations between family members as German bombs fell on London.

Mark Dunton, contemporary history specialist at the National Archives in Kew, south London, said: "You get some sense of Whitehall working at full tilt and people working under pressure and some of the conversations are very tense to say the least.

"It's the sort of dialogue you are used to seeing on films, but this is it for real."