Greville Maynard Wynne 1919 was a British spy who was recruited to MI5 during World War II. He was transferred to MI6 and assisted with the 1959 defection of the Soviet intelligence officer, Major Kuznov.

He was an intermediary for Oleg Penkovsky, who was engaged in selling arms and weapons secrets to British intelligence. Unfortunately, Penkovsky's activities were revealed by Jack Dunlap, a double-agent working for the KGB, who swiftly drew the conclusion that there was a mole in their ranks and set about uncovering him.

The Soviets concluded that one of the likely conduits of information would be a British diplomat in Moscow; George Blake, a Soviet mole inside MI6 had already pointed out Roderick and Janet Chisholm as MI6 operators in the British embassy in Moscow. Penkovsky's visits to an adjacent building identified him as a likely source of the leaks.

Penkovsky was arrested, giving up Wynne's name; the Chisholms were expelled from Moscow for behaviour incompatible with their diplomnatic status.

Wynne was arrested in Budapest and smuggled to the Soviet Union. Wynne was convicted of spying on May 11, 1963 and sentenced to eight years in prison; Penkovsky was sentenced to death and executed. Wynne was released in exchange for the spy Gordon Lonsdale in 1964.