His letter to Mr Fish, dated May 4, 1943, was written from his war bunker in Parliament Street and marked 'secret' in red letters.
'I wonder if you could do a drawing for me of an explosive slab of chocolate,' he wrote. '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.'
He added: 'I enclose a very poor sketch done by somebody who has seen one of these. It is wrapped in the usual sort of black paper with gold lettering, the variety being PETERS. Would it be possible for you to do a drawing of this?'
The letter was found by Mr Fish's wife, journalist Jean Bray, after his death three years ago. Mrs Bray, 80, said Lord Rothschild had told her husband that Churchill and his War Cabinet had been the intended targets.
'Thank goodness we discovered what they were up to,' she said from her home in the Cotwolds. 'If the Germans had been successful, the whole outcome of the war could have been quite different.'
- Daily Mail