The Miniseries:
- Approval of God: John le Carré cited this as his favourite adaptation of his works, attributing this to his experience collaborating with Alec Guinness.
- California Doubling: The Czechoslovakia scenes were filmed in Scotland, mainly Glasgow, but some additional filming in Aberguthrie.
- Creator-Preferred Adaptation: John le Carré was so impressed by Alec Guinness' performance as George Smiley that in later novels he wrote Smiley's characterization to be in keeping with Guinness's performance.
- Dawson Casting: Karla's daughter is supposed to be in her twenties, but the actress playing her in Smiley's People was in her thirties.
- Fake Brit: Control is played by Canadian actor Alexander Knox.
- Fake Nationality: Soviet spymaster Karla is played by none other than SIR PATRICK STEWART. Not that it matters much, since he never talks.
- Hypothetical Casting: Alec Guinness initially felt he was wrong for George Smiley and asked if Arthur Lowe would be more fitting.
- I Want You to Meet an Old Friend of Mine: The cast of Smiley's People includes Michael Gough, who was also in Guinness' films The Man in the White Suit and The Horse's Mouth.
- The Other Darrin: Due to Michael Jayston being unavailable to repeat the role of Peter Guillam for Smiley's People, it was recast with Michael Byrne.
- Playing Against Type: This was a rare dramatic role for Beryl Reid, who was known for light comedy. Alec Guinness was initially opposed to her casting, but she won him over.
- Troubled Production: The series was plagued by a series of strikes. Due to shooting overruns, a large number of actors moved to other projects without finishing their roles. Alec Guinness ended up being on call for eighteen months.
The Film:
- Actor-Inspired Element: 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.
- All-Star Cast: Gary Oldman, Benedict Cumberbatch, Colin Firth, Tom Hardy, Ciarán Hinds, Toby Jones and John Hurt.
- Awesome, Dear Boy: Benedict Cumberbatch stated that playing a spy was his dream job - "you are NEVER what you seem."
- Cast the Runner-Up: John Hurt was an early choice for George Smiley in pre-production, but he was later given the role of Control.
- Dyeing for Your Art:
- Gary Oldman was offered a gray-haired wig to wear for his role, but declined it in favor of bleaching his hair for a more natural hairdo for a middle-aged persona like Smiley.
- Benedict Cumberbatch as well - Guillam's hair is blonde, while Mr. Cumberbatch is naturally a ginger.
- Fake Scot: Toby Jones as Percy Alleine.
- In Memoriam: The film is dedicated to screenwriter Bridget O'Connor, who completed work on the film before her passing away from cancer.
- Playing Against Type:
- Colin Firth and Mark Strong co-star in a movie where one plays a kindly schoolteacher haunted by his past, and one plays a depraved turncoat spy selling international secrets to the Soviets. Sounds pretty typical, unless you know that Strong's the schoolteacher and Firth's the evil spy.
- Gary Oldman is best known for playing very hammy villains, so playing a heroic stoic like Smiley, is a complete 180 for him.
- What Could Have Been:
- Park Chan-wook was offered the film at one point. In 2017 he eventually tapped to direct a six-part Mini Series adaptation of John le Carré's The Little Drummer Girl.
- Michael Fassbender was originally cast as Ricki Tarr, but he had to back out because he was busy filming X-Men: First Class.
- David Thewlis was considered for Roy Bland.
- Ralph Fiennes was considered for Bill Haydon.
- Jared Harris was originally cast as Percy Alleline, but had to drop out because of scheduling conflicts with Sherlock Holmes: A Game of Shadows.
- Word of Gay: In the novel, Peter Guillam was in a relationship with a female musician named Camilla. In the movie, he is a homosexual in a relationship with a man, according to Benedict Cumberbatch, a creative decision that works well within this movie:Sexuality was a very powerful tool then. Guillam keeps his homosexuality secret because he is so open to blackmail. It necessitates a certain amount of secretiveness, which goes hand in hand with spying.
