Sir Nicholas wrote: ‘It is relevant that Mr William Casey, the head of the CIA, who was closely concerned in Cabinet discussion on this subject, has implied to us privately that he thinks the Argentinians may well have been led up the wrong path.

‘They may have believed that their support for the US in covert operations in Central America was more important to the US than in fact it was, and could be expected to earn them American acquiescence in forward policy elsewhere.’

Sir Nicholas also recalled handing US Secretary of State Alexander Haig a piece of paper detailing British evidence of Argentina’s intention to invade on April 2, 1982.

He said: ‘Mr Haig’s reaction to the information I had given him was electric.’

Sir Nicholas added: ‘He wanted us to win and would have been horrified if the Argentinians had got away with it.’