Director Tomas Alfredson based the environment on his first impressions of London when he first visited the city in the 1970s: a brown and grey palette, shadows and uncovered lightbulbs, and dirty streets. "If you see London now and at that time, it's two different cities. Today it's a white city; then it was black; it was so dirty, and you could still feel the War all around."
Gary Oldman went to Old Focals, an eyeglass store in Pasadena, California, to search for the right glasses to fit George Smiley: "Glasses are funny things. For Smiley, they're iconic. It's like Bond's Aston Martin or vodka martini." Oldman tried on hundreds of glass frames before he found the appropriate ones.
John le Carré's novel was based on the uncovering, during the 1950s and 1960s, of the Cambridge Five traitors, who were K.G.B. moles working within the S.I.S. It is the first book in le Carré's Karla, or Quest for Karla trilogy, the second and third parts being The Honourable Schoolboy (1977) and Smiley's People (1979).
To prepare for the role of George Smiley, Gary Oldman ate a lot of treacle sponge and custard to "put on a bit of middle-aged tummy". Oldman also watched Sir Alec Guinness' performance in Calderero, sastre, soldado, espía (1979), and paid a visit to Smiley's creator, John le Carré: "The way he touched his shirt, spoke and so on, I took all that and used it. I hope he won't mind, but Smiley is in his DNA."
John le Carré based the character Karla (Michael Sarne) on the K.G.B.'s Major General Rem Krassilnikov, who was a counter-Intelligence spy for the K.G.B.'s State Security Committee.