Three episodes (The Deserter (1969), The Way Home (1969) and Boys (1969) were made in black and white as the wrong film was used in the location scenes.
Moss Parkin's force identification number (FIN) is 501.
The font used for the credits is Futura Black, designed by Paul Renner in 1929.
Parkin's patch is more accurately the village of Fickley in the North York Moors.