I only ever watched it once, an episode set in Coventry which received a preview in the Evening Telegraph. I can actually remember the TV I watched it on which was B&W Ultra with 23" slimline tube. This was not my usual TV which was away for a repair at the time.
Frank Marker seemed to spend most of the episode in his office making instant coffee which was strange as I was doing the same while watching it! Those were the days when instant coffee was a powder which came in 2oz tins with a foil top which you had to pierce to get at the coffee. If you didn't remove the foil properly it had a habit of flicking coffee powder all over the table!