'John Le Carré''s hero George Smiley was renamed Charles Dobbs because Paramount had the rights to the Smiley name after producing The Spy Who Came in from the Cold the year before - also scripted by Paul Dehn - and later co-produced (with the BBC) the two mini-series with Alec Guinness as Smiley: Tinker, Tailor, Soldier, Spy and Smiley's People. Also re-named was Dieter Freey as Smiley's antagonist, Hans-Dieter Mundt (Peter van Eyck in The Spy Who Came In From The Cold).

Candice Bergen was first choice as James Mason's unfaithful wife.

Freddie Young invented the process of pre-exposing color film (pre-fogging) to mute the colors and first used the process in this movie.

Body count 6.

The ending of this film - somewhat different from that of John Le Carre's original 1961 novel - has Charles Dobbs discovering that the close friend who has been having an affair with his wife is in fact an enemy agent who has cynically initiated the affair as a way of keeping a surreptitious watch on Dobbs's activities. This is very similar to the ending of Le Carre's more famous novel, "Tinker, Tailor, Soldier, Spy", which was not published until six years after the appearance of this film.

The first film of Timothy West.

This is the only film in which siblings Corin Redgrave and Lynn Redgrave both appear.