Based on the same real life events as Another Country (1984), History in Faces: Cambridge Five (2011), Philby, Burgess and Maclean (1977), A Question of Attribution (1991), An Englishman Abroad (1983), Tinker Tailor Soldier Spy (2011), Tinker Tailor Soldier Spy (1979), Blunt (1987), Traitor (1971), Blade on the Feather (1980), The Jigsaw Man (1983) and influenced the source novels of The Fourth Protocol (1987), The Innocent (1993) and others works such as A Different Loyalty (2004) and Olding (2019), even in minor form like in The Imitation Game (2014).
Samuel West, who portrays Anthony Blunt in this series, played the same role 16 years later in season 3, episode 1 of The Crown (2016).
According to website Wikipedia, "the Cambridge Spy Ring was a ring of spies recruited in part by Soviet scout Arnold Deutsch (Otto) in the United Kingdom, who passed information to the Soviet Union during World War II and was active at least into the early 1950s. Four members of the ring were originally identified: Kim Philby (cryptonym: Stanley), Donald Duart Maclean (cryptonym: Homer), Guy Burgess (cryptonym: Hicks) and Anthony Blunt (cryptonyms: Tony, Johnson). Once jointly known as the Cambridge Four and later as the Cambridge Five, the number increased as more evidence came to light."
This mini-series' writer Peter Moffat said of this production: "This is the story of four young but devastatingly effective double-agents who knew from the start that they stood or fell together. Burgess is the loudest spy in the history of espionage, a gifted gob and wicked wit. Philby is the most successful spy of the lot, becoming Head of Counter-Intelligence in MI6. Blunt is cool, viciously funny and clever, while Maclean veers between being warm and friendly and drunk and difficult. Until Burgess and Maclean's desperate flight to Moscow on 23 June 1951 they live in each other's pockets.""
This production's producer Mark Shivas said of this mini-series: "Burgess, Maclean, Philby and Blunt believed that what they were doing was not betraying their country, but serving it. But how long can you hold on to youthful idealism? Peter Moffat's script is about friendship, passion and conviction --- it's about how far they were prepared to go to realise their ideals, and their unshakeable faith in their beliefs."