Most episodes are believed lost, with just 10 of the 39 known to survive. The first six consecutive editions exist - though whilst all were made on colour videotape, the opening five are only monochrome 16mm film prints - plus the final instalment.
Creator Ted Willis (who had earlier devised Dixon of Dock Green (1955) for the BBC) did his research by chatting to the local police force of the North Northamptonshire town of Rushden, the series' filming location for the fictional Broadstone.
A voice-over on the closing credits informed viewers of the first run that "Ewan Hooper is director of the Greenwich Theatre." The actor had been a key component of the Croom's Hill theatre's revitalisation in 1969, and it was even reported that ATV paid his wages for the series directly to the stage group.
May 1975 saw the real-life demolition of Rushden's sub-divisional police HQ, which had served as the Hunter's Walk exterior - the fictional station taking its name from the street it could be 'found' on - since the show began. The interior was faithfully reproduced at ATV's Elstree Studios - and consequently actually outlived its progenitor, albeit briefly.
ATV unit co-ordinator Ben Bentley was responsible for finding all of the locations used in the series.