Previously: The Bletchley Circle. Historical dramas have a symbiotic relationship with costume design, with the clothes in high-profile shows like Downton Abbey receiving almost as much coverage as the stars. I suspect that this is one of the contributing factors to the popularity of historical movies about aristocrats, since it's a lot easier to interview Keira Knightley about corset logistics for the fiftieth time than it is to publicise a bunch of photoshoots of people wearing muddy…