The inability of American officials to provide proper briefings led to an unprecedented breach of protocol – with the US Embassy in London requesting the British account of a meeting between the US President and British Prime Minister.

A confidential memorandum from N.H. Marshall, from the Foreign and Commonwealth Office’s North American Department, outlined the incident in June 1984 – relating to a meeting between Margaret Thatcher and Ronald Reagan.

The document, which was released to the National Archives by the FCO this week, stated: “Mr McCormack in the American Embassy telephoned a few days ago on behalf of his Ambassador. He said that Mr Price had asked him to see whether the Foreign Office could let the Embassy know what the President and the Prime Minister had talked about, because he 'did not get a very good read-out'".

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It added: “Mr McCormack made it clear that he was somewhat embarrassed to put this request to me.”

The FCO official commented: “I am not sure what to make of this”, but added: “It is certain, however, that the president’s report of his conversation to his aides will not have been anywhere near as good as the prime minister’s account summarised in Mr Coles’ letter of 5 June.”

Downing Street would not “normally contemplate the disclosure of our record of a tete-a-tete meeting with a visiting head of government".

However, the official suggested: “It is for consideration whether we could profit by Mr McCormack’s invitation in order to reiterate to the Americans on official channels any points made by the prime minister to which we attach particular importance and which may not have been fully received by the Americans.”

But the civil servant, having looked at the account of the meeting, concluded: “There is nothing in this record of such importance to us that we would want to take the unusual step of discussing No 10’s record with the Americans.”