When the urbane English actor met one of the country's most notorious traitors, the Security Service MI5 was desperate to find out all it could about what passed between them.
Over Christmas of 1958, Michael Redgrave - one of Britain's biggest stars - was leading the Shakespeare Memorial Theatre Company on a rare tour behind the Iron Curtain to Russia.
There, in Moscow, he encountered his old friend from Cambridge - Guy Burgess who had fled there seven years earlier with his fellow Foreign Office diplomat and Soviet double agent Donald Maclean, in one of the biggest spy scandals of the Cold War.
Details of their unlikely reunion are revealed in newly-declassified MI5 files released by the National Archives in Kew, west London.
It did not get off to a good start, with the louche, flamboyantly homosexual Burgess turning up drunk at the theatre where Redgrave was starring in a production of Hamlet.
"We also heard that after one of the performances Burgess made his way to Redgrave's dressing room and there was sick," the British ambassador Sir Patrick Reilly reported.
Nevertheless, Redgrave agreed to visit Burgess for lunch in his flat - which had been provided by the KGB following his defection - much to Sir Patrick's chagrin.
"Redgrave was not very communicative about this meeting and did not consult anyone in the Embassy before meeting Burgess," he complained.
Burgess, however, clearly enjoyed their get-together writing to his mother in London - in a letter intercepted by MI5 - that they had had "fine gossips".
He gushed about Redgrave's acting: "I have never seen such a reception as Michael's Hamlet got on its last night.
"It's certainly the best Hamlet I've ever seen - better than Gielgud, better than Olivier, much better than Paul Schofield. And everyone here thought the same too."
Burgess also described how he had befriended another member of the cast, actress Coral Browne - an encounter later dramatised by Alan Bennett in the television play, An Englishman Abroad, starring Alan Bates.
"I thought Coral Browne was a dear - but people often think that of actors and actresses when it is in no way reciprocated," he wrote.
Browne, however, proved as good as her word, honouring a promise to buy Burgess a set of eight new suits from his London tailor and send them on to Moscow.
MI5, on the other hand was interested in rather weightier matters. Redgrave - the father of the actors Vanessa, Corin and Lynn - had first come to their attention in 1940 when he signed the manifesto of the Communist-inspired "People's Vigilance Committee" and they were keen to know what the two men had discussed.
Their curiosity was further whetted by a chance meeting at the Savile Club between MI5 officer Cedric Cliffe and a friend who knew Redgrave and had spoken to him about his meeting with Burgess.
Much of what Burgess was said to have told the actor they already knew - that he was "miserably unhappy" in Moscow, despite having been provided with a comfortable house, a housekeeper, and a "boy friend" who also apparently doubled as a "state security spy".
Cliffe was however intrigued by one reported remark by Burgess - "I did all that was required of me by bringing Maclean safe to Russia."
What MI5 did not know was that the two diplomats' flight had been prompted by a warning from their fellow Soviet spy Kim Philby - who had become a high ranking officer in MI6 - that Maclean was about to be unmasked as a traitor.
However when Burgess went with Maclean - who was close to a nervous breakdown - his close friendship with Philby meant that Philby too had quickly become a suspect.
In his memoirs following his own defection in 1963, Philby said he had urged Burgess not to follow Maclean to Moscow, knowing that he too would be compromised
A further meeting between Cliffe's source and Redgrave confimed Burgess had not wanted to defect - believing his own role was simply to get Maclean safely out of the country - and that he had been duped by his KGB handlers.
"Redgrave told source that Burgess had more than once told him that he, Burgess, had considered that he had done his bit (or words to that effect) in delivering Maclean to the Russians," Cliffe reported.
"Burgess also said that he himself had not intended to go to Russia once he had introduced Maclean to persons whom he met 'at a certain place'.
"Burgess said that in spite of his wishes he had been forced to continue his journey and ended up in Russia."
As his KGB handler Yuri Modin later admitted, Mosow had concluded that it had two "burnt out" agents on its hands and it could not afford to leave Burgess behind.