George Segal was the first actor to play the character Quiller in film and TV and is the only one to ever play him on the big screen. Michael Jayston is the second and last actor to play Quiller, having played him in the TV series Quiller (1975).
This espionage film's score was composed by John Barry who became notable for the early James Bond spy film soundtracks. Barry composed the score for this film between the Bond movies Thunderball (1965) and You Only Live Twice (1967).
In adapting Adam Hall / Trevor Dudley Smith's novel "The Berlin Memorandum", Harold Pinter largely altered the emphasis of the book to be less of a spy thriller and more of a meditation on the human condition and the duplicitous nature of identity.
The theme music played throughout the film was recorded by Matt Monro as "Wednesday's Child". The song is playing on the radio in the reception of Quiller's hotel and appears on several of Monro's albums.