A NAZI plot to use exploding bars of chocolate to kill members of the wartime cabinet has been uncovered in the Cotswolds.

Jean Bray, of Hailes Street, Winchcombe, discovered secret wartime letters when she was sorting correspondence belonging to her late husband, Laurence Fish.

The letters were between Lord Victor Rothschild – one of MI5’s most senior intelligence chiefs – and her husband, who was an artist working in his unit.

In one of the letters Lord Rothschild, who headed the countersabotage department, asked him to draw images of the chocolate bars to alert those in the field who might find them after a sharp-eyed British spy spotted one and raised the alarm.

Stamped “SECRET” in red letters and written from Lord Rothschild’s bunker in Parliament Street, London, the letter says: “Dear Fish, I wonder if you could do a drawing for me of an explosive slab of chocolate.

We have received information that the enemy are using pound slabs of chocolate which are made of steel with a very thin covering of real chocolate.

“Inside there is high explosive and some form of delay mechanism, but we do not know what.

When you break off a piece of chocolate at one end, instead of it falling away a piece of canvas is revealed. When the chocolate is pulled sharply the canvas is also pulled and this initiates the mechanism. After seven seconds, the bomb goes off.”

Jean, aged 80, said she found them when she was sorting through the late artist’s papers to write about his life and work for her book Pick Up a Pencil.

“I have tried to find out more about this letter and the others I have from the period but I haven’t had any luck,” she said.

“Laurence knew Lord Rothschild quite well. After the war he went back to Cambridge to do his scientist work and got him to do some drawings for him.”

The exploding bars were packaged in expensive-looking black and gold paper and branded as Peter]s Chocolate. The aim of the plot was for the bars to be taken into meetings of the British War Cabinet, targeting high-ranking officials and even Winston Churchill.

But the plot was foiled by British intelligence before the bars could pose any danger to the wartime Prime Minister.

Lord Rothschild valued Laurence’s work so much that he included a section called Fish Junior in his book Random Variables but Jean said her husband never knew about it.

Laurence lived in Winchcombe for the last 15 years of his life and died in 2009 aged 89.

His commercial work and fine art has been on display at the Winds of Change Gallery in Winchcombe.