The first two series were shot mainly in a studio on videotape with filmed location inserts; a standard method of the time but one which suffered from jarring differences in picture quality between interior and exterior scenes. The location scenes of some episodes were shot on outside broadcast cameras, leading to smoother transitions between location and studio work for those episodes. Series 1 and 2 starred Derren Nesbitt as Det Insp Jordan, working to Det Supt Eden (Wensley Pithey) and subsequently Det Supt Inman (Fulton Mackay). The episodes featuring Eden (the first 9 of Series 1) were recorded in black and white, while all subsequent episodes were recorded on colour videotape.
The show was revamped in 1973 after Thames Television's Euston Films Limited subsidiary took over production using film which allowed for a less studio-based series. Euston Films had pioneered the technique of shooting action and adventure series entirely on location using 16mm film, for a more gritty and realistic look. These episodes starred George Sewell as Chief Inspector Alan Craven and Roger Rowland as Bill North. The show was slow to take off so the producers introduced Patrick Mower as Detective Chief Inspector Tom... Read More