I am a huge fan of both the Karla Trilogy books and the 2 BBC series which followed. Smiley's People in particular is just exceptional in all ways. Faithfully captures the drama and detail of the book. Fabulous cast of Brit and Continental actors headed up, of course, by Alec Guiness, who perfectly captured the essence of Smiley. A couple of my favorites in the supporting cast were Bernard Hepton as Toby Esterhase and Michael Lonsdale as the hapless Soviet diplomat Grigoriev, both of whom adroitly sprinkled their dramatic performances with subtle humor.
This was a low budget BBC production, so don't look for flashy sets or cinematography, just brilliant acting, intelligent dialogue, suspense, and atmospheric background music.