The recent death of Edward Woodward brought back to mind the swinging light bulb of Callan.
In the late sixties/early seventies Britain made downbeat telly programmes with stories of corruption and seediness, visual Graham Greeneland minus the Catholicism. We saw them in New Zealand years after they were made. We were always way behind. Pallid immigrants from Britain would arrive with news of what was going to happen in Coronation Street. These programmes of greyness and griminess contrasted with the brash, action-filled American shows and their abnormally good-looking actors. I can't remember when we got a colour telly, but the colours of the British shows were so subdued anyway compared to the bright American shows that they may as well have been in monochrome.
Villains was another series of that era with the same kind of atmosphere. Does anyone remember it? Google hardly seems to have heard of it.
There was also Law and Order – not the American show, but a short series about crooked cops and dodgy solicitors. The American show makes it difficult to find it on Google but I bet it was made about then as well.
The Sweeney came along a little later. The final rolling credits over the mournful theme tune and the moral ambiguity make it look like son of Callan.