The latter veneration of his TV work seems to me to have obscured some of his astonishing work in other series and TV work.
REDCAP was my first exposure to John Thaw. A young, raw and angry actor - who my own Dad COMPLETELY identified with at the time of the series' showing. Dad was an ex-soldier, with no love of military policemen. But he used to let me stay up late to watch REDCAP, because he was so taken with Thaw's portrayal of a FAIR army cop. Angry, aware of what he had to do, aware of his subordination to senior officers (who often pulled rank in the episodes, despite the justice of the case) Thaw's performances were utterly compelling. I hope someone reads this review, has some clout - and could bring 'em out on video/DVD, whatever.
Last throwaway point to anyone wanting to follow-up John Thaw's acting power prior to the MORSE years.
Check out if you can, a British television production of MACBETH from the 60's/70's starring Eric Porter - which has John as the scariest Banquo's ghost you've ever seen.