Callan

Lonely Did you shoot him, Mr Callan?
Callan No. I hit him, and he died of it.

British spy series that ran four series on ITV, from 1967 to 1972. Edward Woodward is the eponymous hero, David Callan, an agent employed by "The Section", a shadowy arm of the British intelligence services during the Cold War. Callan was introduced in a one-off play, "A Magnum for Schneider", which became in effect a pilot for the series; there was also a movie and a reunion episode, "Wet Job", in 1981.

The Section specializes in disposing of enemies of the state by dubious methods like blackmail, extortion and murder, and Callan is its most highly regarded operative. He is helped and hindered in his work by his boss, code-named Hunter except for a brief period during season 4 when Callan is Hunter, fellow agents such as the sadistic Meres and the cocky Cross, and a malodorous little small-time crook named Lonely.

Tropes used in Callan include:

Anti-Hero: Callan himself, as well as Hunter, at least as played by William Squire in seasons 3 and 4.
Anyone Can Die: There was an episode entitled "Let's Kill Everybody!". It pretty much lived up to its title.
Berserk Button - Don't touch Callan's model soldiers.
Black and Grey Morality: Callan has a conscience but it doesn't stop him doing a pretty unpleasant job. He's just too scared to quit.
Deadpan Snarker - Most of the cast, but Callan in particular.
Everyone Calls Him "Barkeep" - The head of the Section is always called "Hunter" and never known by any other name except of course for Callan himself in season 4.
I Did What I Had to Do - On more than one occasion Hunter makes it clear that he doesn't like the orders he's giving Callan any more than Callan does, but he expects them to be carried out nonetheless.
Incredibly Obvious Tail - Justified when agents follow a Russian diplomat around in order to harrass him.
Kick the Dog - Callan has to "Rebuke" Lonely on occasion. On the other hand...
Make It Look Like an Accident - The Section is not above arranging this.
Pet the Dog - ... Callan also does his best to protect the little man.
The Pig Pen - Lonely
Pointy-Haired Boss - Both played straight and averted; some of the Hunters are a good deal more capable than others.
Prisoner Exchange - The opening episode of season 4.
Sliding Scale of Cynicism Versus Idealism - Pretty cynical on the face of it, although Callan's insistence on knowing what his intended victims have done suggest he is more idealistic than he cares to admit.
Spy Fiction - the bitterest of Stale Beer. Even more so than The Sandbaggers in a way, since Burnside at least believes in what he does, while Callan only does it because he'd be unemployable in any other job, and the Section would probably have him killed if he tried to quit.
The Spymaster - The Section's Boss, Hunter, and his boss, Bishop.
Spy Speak - The KGB are "The Opposition" for example.
Tyrant Takes the Helm - On finding out that the original Hunter, played by Ronald Radd, has been temporarily reappointed, Callan is so appalled that he promptly announces he's going on leave. Needless to say he isn't allowed to.
What The Hell, Hero? - As cold blooded murder is in Callan's job description, instances of this hardly stand out, but systematically wrecking a couple's marriage to facilitate a defection in "The Little Bits and Pieces of Love" probably counts.