A misjudged prank recording which appeared to show US president Ronald Reagan at odds with Margaret Thatcher almost sparked an international incident, confidential documents have revealed.
The tape, supposedly a recording of President Reagan and the then prime minister arguing over the progress of the Falklands War, was sent to a number of Dutch newspapers during the 1983 British general election.
Submitted anonymously, a transcript claimed the president urged Mrs Thatcher "to control yourself", to which the Iron Lady responded: "We have to use violence (on Argentina). At this moment it is being used to punish them as quickly as possible."
The staccato exchange allegedly began: "R: I urge you to control yourself. That's absolutely necessary, for otherwise the area will be devastated.
"T: Listen, our goals are completely different.
"R: Why was the Belgrano destroyed? You gave the orders to do it. The Argentines were leaving at the time."
The audio and attached letter were quickly handed to the authorities and dismissed as a forgery.
Contemporary reports credited the work to punk-rock band Crass, but, according to Foreign and Commonwealth Office (FCO) documents released today, the government feared more subversive forces were at play.
In one letter, sent by an FCO adviser to Mrs Thatcher informing her of the incident, MI6 seemingly considered blaming the Soviet Union, Argentine secret services and left-wing radicals.
It stated: "The embassy in Hague recently passed to London a tape recording of a purported telephone conversation between the Prime Minister and President Reagan during the Falklands crisis.
"This looks like a rather clumsy operation. We have no evidence so far about who is responsible. SIS (Secret Intelligence Service, commonly known as MI6) doubt whether this is a Soviet operation. It is possible that one of the Argentine intelligence services might have been behind it; or alternatively it might be the work of left-wing groups in this country."
Another briefing from the FCO, on April 6 1984, focuses on news reports that the tape was the work of the KGB, the Soviet Union's secret police.
"The Daily Telegraph of July 28 reported that the (US) State Department suspected KGB 'disinformation'," it said.
"Neither our friends nor CIA (Central Intelligence Agency) considered this very likely, but further analysis would have required a disproportionate commitment of resources which even CIA felt unable to contemplate."
The tape was exposed as a forgery through analysis by MI6, the CIA and Mrs Thatcher's closest political advisors.
According to a letter sent from Downing Street to the FCO, the recording was made with "voice-patch" technology, with which the forgers cut together clips of the two leaders from public interviews.
The alleged conversation mimics in parts answers Mrs Thatcher gave during a BBC Panaroma interview in April 1982, including the phrases "Argentina is the invader" and "force has been used".