After watching the early rushes of Tinker Tailor Soldier Spy (1979), John Hopkins and John le Carré re-drafted the script of this series to subtly change George Smiley's character to use Alec Guinness's performance to greater effect.
Although the standard for British TV miniseries in the 1970s-80s was to videotape interior scenes and film exteriors, all of this miniseries was captured on film.
During its original airing on BBC television radio DJ Terry Wogan ran a "Does anyone know what's going on?" competition on a weekly basis. This amused John le Carré greatly.