Indeed, I do know it, and I have a DVD boxset of The Sandbaggers stored away. That said, I've only watched it once, probably around 15 years ago now, so perhaps it's time for me to revisit it.
It was made by Yorkshire TV for the ITV network, and as was the style at the time for most UK dramas, location work was shot on film, but studio work was shot on video tape. I think in many viewers' eyes, that lowered its "quality" a bit, but it was highly regarded and Roy Marsden is excellent. He would go on to star as Det Inspector Adam Dalgleish in Anglia TV's adaptation of PD James' detective novels in which he played an erudite detective - a sort of precursor to Morse. (Note the Dalgleish novels have been revisited in more recent times).
I think The Sandbaggers isn't as well remembered because a year after its 1978 debut, the Alec Guinness version of Tinker Tailor Soldier Spy came out and that was really a high water mark for cold war spy stories of the era. It was a co-pro and so was fully shot on film. It was based on John Le Carré's highly regarded novels and of course it starred Guinness, who was a massive star appearing in everything from Ealing comedies through to Doctor Zhivago and Bridge on the River Kwai. And of course, most recently at that point, Star Wars. Plus, big movie stars didn't do TV at that time, so getting him to make Tinker Tailor, and then afterwards Smiley's People, was a massive coup.
I guess that you've seen both of those, but if not, do find them. They both remain for me some of my favourite dramas from the 70s and 80s, and it annoys me sometimes that people think that TV didn't do serious stuff really well until The Sopranos. They've been restored for Blu Ray so the HD versions look fantastic. And also check out 1987's A Perfect Spy which is also excellent, based on Le Carré's most autobiographical novel.
Adam