Designing costumes for spies isn’t easy: If they’re good agents, after all, you don’t know anything about them—least of all what they look like. But that’s what Jacqueline Durran had to do as head costume designer for Tinker Tailor Soldier Spy, the new film adaptation of John le Carré’s classic cold war novel set to open in December. The five main characters are suit-clad MI6 operatives. “Not having reference material to go on was the biggest challenge,” Durran says. “Obviously, there aren’t many photos of MI6 members, so it was hard to know what they wore.” To engineer menswear that would transport viewers back to 1973 England, she turned to tailoring magazines and pictures of politicians from the time: upper-middle-class conservative white dudes who wore bespoke suits and bought their watches and ties at London’s Burlington Arcade. Here’s how Durran, whose costumes for Atonement and Pride & Prejudice earned her Oscar nominations, styled George Smiley (played by Gary Oldman), the top spook on the hunt for a Soviet mole.

• The specs: Oldman found his own glasses at a vintage store in LA—he wanted frames similar to the ones Alec Guinness wore in the original 1979 TV miniseries adaptation.
• The shirt: Traditional single-cuff (French cuffs would be ostentatious) and with a formal collar shape—none of that disco-batwing ’70s stuff.
• The tie: Only in restrained colors. This one is made from English silk, since a conservative middle-aged man would’ve supported classic British goods rather than pick a tie of trendy imported Indian silk.
• The suit: A gray three-piece in a formal style. At the time, tailors were plentiful, and off-the-rack suits weren’t the norm yet, so Durran had the suit cut and sewn by hand at British suitmaker Timothy Everest.
• The buttons: Back then, a quality suit came with buttons made from cow bones; Smiley’s are cow horn, dyed gray to match the suit.
• The scarf: Cashmere, also in muted colors and woven in Scotland.
• The trench coat: A traditional Mac material and color: beige with gray lining. To get the style right, Durran consulted the archivist at the classic British haberdasher Aquascutum, which re-created a 1970s coat for the film.