Declassified documents reveal how British spies hunted in vain for the creator of a fake recording of a spat between British Prime Minister Margaret Thatcher and U.S. President Ronald Reagan.

Soviet spies, Argentine agents and British leftists were considered to be the possible pranksters but an anarchist punk band later claimed responsibility.

The tape, sent to Dutch newspapers in 1983, purported to capture the leaders sparring during the 1982 Falklands War. A transcript shows Reagan urging Thatcher "to control yourself," and the British leader responding: "We have to use violence" against Argentina.

British authorities quickly identified the recording as a forgery.

The punk band Crass later said it had been responsible.

The papers were released Friday by Britain's National Archives as it declassifies some government documents over 30 years old.