The agent's identity remains a secret, the Daily Mirror reported. He is identified only by the nom de guerre "Jack King" or the initials S.R.
The latest document dump from the National Archives also shows that MI5, Britain's domestic intelligence agency, tracked artistic luminaries, including actor Michael Redgrave, writer J.B. Priestley and two leading musicians, composer Benjamin Britten and his longtime musical and romantic partner, tenor Peter Pears, the Guardian said.
King's network was a mix of immigrants who were in Britain when the war began and native-born Nazi sympathizers, the Mirror reported. Marita Perigoe, who left the British Union of Fascists because she considered it too centrist, gave King her unwitting help, bringing those who agreed with her into the group, documents show.
MI5 even faked Iron Crosses, Germany's highest military decoration, and gave them to some of the spies for their work. The agency discussed creating a badge to be distributed to King's organization, ostensibly so German troops would recognize them after an invasion. In fact, the badges would have identified them for a British roundup.
King's group was actually kept going for a few years after the war just in case. In the end, British officials decided against arresting and trying the spies.
The documents show that Pearson, Britten, Priestley and Redgrave were tracked for quite a few years, with MI5 reading their mail and listening in on phone calls.
Redgrave's file includes a letter Guy Burgess, one of the Cambridge spies, wrote his mother from Moscow, describing a lunch with Redgrave, who was starring in "Hamlet" there. In the letter, Burgess called Redgrave "an old friend from Cambridge days" and described his Hamlet as a "triumph."
Burgess also told his "darlingest Mum" that Coral Browne, who was also in the play, had offered to buy him some suits.