Death by Chocolate

Explosives covered in chocolate, or hidden in everyday items such as soap, thermos flasks or tinned food -- as with everything, Nazi saboteurs worked out their schemes to smuggle bombs into Britain in exacting, but futile detail.

British intelligence files released in the last six months provided details of the plots accompanied by diagrams of "devices that were supposed to cause mayhem on this island," said Professor Christopher Andrew, who is writing a history of MI5, the British domestic intelligence service.

But they were never carried out successfully.

"As far as we know there was never any successful sabotage by German agents in the UK during the war," archivist Howard Davies said.

The intelligence files suggested that the explosives-packed products were bombs in themselves, possibly targeting consumers. But Davies said he believed the real intention was to smuggle in explosives for industrial or military sabotage.

Chocolate bomb

"The bomb is made of steel with a thin covering of real chocolate," said a note accompanying a diagram of an exploding chocolate bar. "When the piece of chocolate at the end is broken off the canvas shown is pulled, and after a delay of seven seconds the bomb explodes."

Other plots were evident from photographs of explosives disguised as tins of Amieux Cassoulet stew and Smedley's English Red Dessert Plums.

Explosives in lumps of coal, car batteries, tins of fish in tomato sauce, boot soles and heels, pencils and fountain pens were among other exhibits shown.

And perhaps the most stomach-turning smuggling device? A "rat stuffed with explosive and fitted with time pencil," a file said.