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.

First theatrical movie directed by screenwriter Dick Clement.

One of several espionage/government agency comedies and parodies directed by Dick Clement, and mostly co-written by Clement with Ian La Frenais. The others include Catch Me a Spy (1971), Bullshot Crummond (1983), and Water (2005).

This movie was released three years after its source novel of the same name by Martin Waddell was published. "Otley" was Waddell's first published novel, and this is the only filmed adaptation for the cinema from a story or stories by the writer. The other three, all published in the next consecutive years, include "Otley Pursued" (1967), "Otley Forever" (1968), and "Otley Victorious" (1969).

One of three consecutive espionage movies that cinematographer Austin Dempster shot back-to-back-to-back around 1968-1969, the others being A Dandy in Aspic (1968) and The Looking Glass War (1970).

The only filmed adaptation for the cinema from a story or stories by Martin Waddell.

Both movies in which Sir Tom Courtenay appeared in 1968 were espionage movies, this movie and A Dandy in Aspic (1968).

Tom Courtenay (who was not yet Sir Tom Courtenay) had worked with Leonard Rossiter in Billy Liar and King Rat; James Villiers in God & Country; and James Bolam in The Loneliness of the Long Distance Runner.

There's a poster of a George Peppard movie (P.J. (1968)) when Otley enters the train station. Tom Courtenay had appeared with Peppard in Operation Crossbow (1965) a few years earlier.

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.

The name of the agency, for which Gerald Arthur Otley (Sir Tom Courtenay) worked, was Department M-2 of British Intelligence.

The full name of Otley, played by Sir Tom Courtenay, was Gerald Arthur Otley.

The odd "Otley" title refers to the last name of the central character played by Sir Tom Courtenay. There is no connection with the small town in West Yorkshire.