Tom Courtenay (who was not yet Sir Tom Courtenay) had worked with Leonard Rossiter in Billy Liar (1963) and King Rat (1965); James Villiers in King & Country (1964); and James Bolam in The Loneliness of the Long Distance Runner (1962).
A spoof of that era's spy movies, the main henchman is ironically played by Robert Brownjohn, who did the opening credits for From Russia with Love (1963) and Goldfinger (1964). He also did the credits for The Night of the Generals (1967), co-starring Tom Courtenay.
During the beginning tracking shot of Otley walking down the street (while the song "Homeless Bones" plays over the opening credits), most of the people on the street wind up staring into the camera, as if they just realized a film was being shot.
Tom Courtenay, playing everyman Otley, pokes fun at the fact a particular character will soon be knighted (making a noise and expression as if that were pretentious or conceited). Years later, in real life, Tom would become Sir Tom Courtenay.