Tinker, Tailor, Soldier, Spy.
BBC iPlayer has the original series of this adaptation of John Le Carré's book ready for downloading. This is the series starring Alex Guinness, Hewell Bennett, Beryl Read, etc and was fabulous TV in its day.
I've already downloaded all 7 episodes and we've watched the 1st 2. It hasn't lost any of its original production values imho and is well worth watching again even though it's not available in wide-screen.