Tinker Tailor Soldier Spy Costume

I've described Tinker, Tailor, Soldier, Spy to friends as "a movie about grey-faced men in suits looking at each other suspiciously", although a slightly more accurate description would be that it's a British spy thriller set in the 1970s, starring Gary Oldman as a spy brought out of retirement to track down a double agent in the upper echelons of MI6. It's full of reticent Englishmen (Colin Firth, Benedict Cumberbatch, Tom Hardy...) staring at each other expressionlessly as they try to figure out who is double-crossing whom, and it's freaking awesome. (N.B. Don't worry -- this post is spoiler-free.)
No one in Tinker, Tailor is dressed ostentatiously, and it would've looked out of place if they had been. The setting is (mostly) London in the early 1970s, but it's not the '70s of David Bowie, it's the '70s of chilly civil service offices during the Cold War, where feminism hasn't really hit yet. There are women working at MI6, but they're mostly office aides working silently in the background.
George Smiley
Gary Oldman's character may be the focus of the story, but he's as sombrely dressed as he is quiet in personality. He's neat, he's efficient, he's dogged, and his clothing gives away about as much as his complete lack of outward emotional expression.
According to an interview with the costume designer, Gary Oldman wears two (very similar) grey suits in the film, but I'm damned if I can tell the difference. Everything about him is designed to fade into the background. He's one of the old guard of British spies, quiet men who lived through the War and are slightly out of place in the changing world of the 1970s.
The one time we see him make contact with the world outside the Cold War machinations of "the Circus" (British Intelligence's nickname for itself) is when he goes to meet with his former colleague at her new job, running a hostel for students:
Check out how 70s her shirt is! Is that an artificial fibre I see? (Gary Oldman, on the other hand, looks like he only just noticed that WWII rationing is over.) I loved this scene for its juxtaposition of the buttoned-up Smiley and the young, hippie-ish kids dressing up and fooling around nearby in the hostel.
Guillam
Guillam, played by Benedict Cumberbatch, is Smiley's second in command and the youngest of those working at MI6. He's a bit more modern, and unused to the ruthlessness of the older agents who already lived through one World War.
His trousers have got a bit of a flair. His hair is more modern than that of the other agents. Compared to the older men, who have been wearing either rigid woollen school uniform, rigid woollen military uniform or three-piece suits since birth and have never once considered the possibility of self-expression, he's practically a dandy.