If you can find it, the the Sandbaggers was an interesting series. I really got hooked on it.
Sandbaggers is a first rate series.
I did, too. But it got too depressing for me, eventually.
https://www.youtube.com/watch?v=Unpk5X2HuJw
On the other hand, it was popcorn to Callan.
https://www.youtube.com/watch?v=wGF5BS937yU
Edward Woodward played a role that looked like the precurser to The Equalizer. He was an alcoholic assassin who becomes spymaster himself and is given a red file to kill his best friend. Ah, British TV shows. Often depressing but also addictive.