By her own admission, Kristin Scott Thomas was famously difficult on set whilst working on the film. In an interview with a British newspaper in 2005, she said that "when I did Gosford Park (2001) with Robert Altman, apparently I was a complete nightmare. I was very imperious and completely foul and horrible. And I had no idea I was doing it at all. Actually, that's not entirely true; I did wonder why people were giving me sideways looks, and there would be this odd hush whenever I walked into a room. The only explanation I could come up with was that I was half in character the whole time. I was playing this woman who was difficult and so I became difficult. But I did apologize to everyone afterwards."
In the DVD commentary, director Robert Altman states he included the F-word several times on purpose to get an R-rating because he didn't want kids to see the film - he thought kids wouldn't like the film so he wanted to keep them out (especially 14-year-old boys).
This movie is singular in that no fewer than six British Knights of the Theatre are in the cast: Alan Bates, Derek Jacobi, Michael Gambon, Eileen Atkins, Helen Mirren, and Maggie Smith all have received the highest national honor for contributions to drama.
During group scenes, director Robert Altman had two cameras going at all times, moving about (out of each other's shot, of course). His intention was to prevent the actors from acting to the camera but instead to play the scene more naturalistically.
The wallpaper in Constance Trentham's bedroom is hand-painted, imported from France. Even for this very small set, it would have cost the filmmakers $18,000; however, the manufacturer donated it to the production. Even so, the owners of the house demanded that the walls were re-papered to their liking (to match their bedding) after the production was over.
Maggie Smith plays an aristocrat who looks down on her maid, though she played a lady's maid to a snobby aristocrat played by Bette Davis in Death on the Nile (1978), and Davis similarly played a deranged governess to an upper class family in the chiller The Nanny (1965).
Bob Balaban recommended to Robert Altman that Julian Fellowes write the screenplay. "Altman asked him to try it, and maybe six weeks later Julian sent the first 75 pages. It was clear that he was brilliant and his knowledge of class society, the workings of it, was encyclopedic. This talented writer, moldering away as a relatively unsuccessful actor! That was a brass ring, and he took it. It's part of the key to his current success, his work ethic. He doesn't procrastinate. He doesn't hide. He works like a demon." (Alex Wichtel, NYTimes 9/2011)
Altman consulted the writer Ezna Sands in depth on the idea before commencing with the project, having wanted to employ his doctoring skills on the script. Sands simply said it was as close to perfect as it could possibly be.
Rather than just use a typical boom mike to pick up dialogue, Altman had all the actors wear portable microphones to assist in creating overlapping dialogue. A technique he first developed during A Wedding (1978) and has used several times since.