The TV series really were perfection and not just down to Sir Alec Guinness. Ian Richardson, Bernard Hepton, Michael Jayston etc were all wonderful - not to mention Arthur Hopcraft's adaptation. The opening scene with four men, an office, no action and four words of dialogue, yet a world of detail sets the tone for the rest of the series [1]
Recently re-reading TTSS with Alec Guinness's Smiley in my imagination was a wonderful experience. Thank you John Le Carre.
PS One oddity is that in TTSS Toby Esterhase has a British accent but in SP he's acquired a broad Hungarian one!