The character of George Smiley, John le Carré's hero, was renamed Charles Dobbs for this movie. This was because Paramount Studios had bought the rights to the Smiley name when they produced L'espion qui venait du froid (1965).
John le Carré was not wildly impressed by this screen adaptation of his novel: 'It had a cast to dream of: Mason, Maximilian Schell, Simone Signoret, Harry Andrews, Roy Kinnear - not to mention a beautiful young female Scandinavian actor who to my astonishment stripped naked, which in the Swinging Sixties was a kind of necessary dare [i.e. Harriet Andersson]. The sight of her so impressed me that I left the cinema thinking of little else. When I came to my senses, I had an impression of an assembly of nicely shot cameos that didn't quite add up.'
In this film, James Mason was the second actor to play John le Carré's famous George Smiley character on screen and TV though the character was renamed Charles Dobbs for this movie. Rupert Davies was the first actor to play him in L'espion qui venait du froid (1965); Sir Alec Guinness was the third, he played him twice, in La taupe (1979) and Les Gens de Smiley (1982). Denholm Elliott was the fourth actor to play Smiley in Les chandelles noires (1991), whilst Gary Oldman is the fifth actor to play him, in La taupe (2011).
Cinematographer Freddie Young invented a process of pre-exposing color film negative to a controlled small level of light to mute the color. This process was called pre-fogging or flashing and this was the first-ever film to use this. This movie's director Sidney Lumet labeled the process "colorless color".
The film's source novel title "Call for the Dead" was changed to "M.15 demande protection (1967)" for this film, as it was a more commercial title.