I don’t know how far back we’re allowed to go. I’ll second the recommendations of Wolf Hall and Brideshead Revisited.
If time isn’t a factor, then there’s a lot of great Masterpiece Theater/BBC type stuff, particularly the 1980 Pride and Prejudice and Tinker Tailor Soldier Spy, and the 2005 Bleak House.
What I consider the greatest fictional and nonfictional TV shows of all time, respectively, both aired on PBS at some point: I, Claudius and Carl Sagan’s Cosmos.
I, Claudius was great, and had some amazing performances, but its production values left something to be desired. It looked like an old-school videotaped soap opera–more like a televised play than anything else. If only it had had the budget of HBO’s Rome…
Production values were bare-bones, but that vanishes into irrelevancy for me next to the writing and acting, which is miles beyond Rome (itself a fine show, with first-rate production design as you say).
My local PBS station used to just do BBC shows on Sunday, although they did British comedies on Friday nights. I see now they are doing them all night Thursday’s and part of Wednesday’s.
What do I watch on PBS? Frontline mostly, Nova depending on the topic and often whatever is on the American Masterpiece series (is that what it is called?).