British TV Spy Series 1980s or 1990s

[devinsong]

I've been racking my brain (and scouring the internet) trying to find a British TV espionage/spy series I saw in the late 80s or early 90s. It aired in the US on PBS. The main character was middle-aged and had a very common name- Mr. Smith, Jones, Johnson, something like that. He was working in an office in England with younger agents who tended to dismiss him as uncool, out of date and over the hill. They were tasked with counterintelligence, I think. He gets partnered with a very green young agent who is shocked by his casually doing very illegal things in a quiet and unassuming way. Their superiors may have quietly routed the tricky assignments to the experienced guy because they knew he could make problems go away.

I remember it as being around the same time as Sleepers, but later (and having a more modern style) than Sandbaggers (and not either of those shows). Anybody got a guess?