Dudley Sutton (Deller) and Colin Campbell (Det. Insp. Terry Potter) previously co-starred in The Leather Boys (1964) as Pete and Reggie, leaders of a motorcycle gang.
Colin Campbell (Det. Insp. Terry Potter) previously appeared with John Thaw in Paterson's Private Army (1966)
When Carter is following Fuller and Deller in clear dry weather, the sound of a thunder storm had to be dubbed over the scene to explain why, in the very next shot (obviously filmed later) it is suddenly pouring with rain and clearly has been for some time.