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).
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."
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.
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.
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)
The TV series Downton Abbey (2010), written and created by Fellowes, was originally planned as a spin-off of Gosford Park, but instead was developed as a stand-alone property inspired by the film, set decades earlier.
In the documentary Altman (2014), it is stated that Robert Altman was unable to fund this movie, even with most major stars not being paid and lining up to work with him. Eventually he said he won the lottery when the British Lottery funded the film.
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.
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). Davis similarly played a deranged governess to an upper class family in the chiller The Nanny (1965).
Although the film takes place in 1932, Ivor Novello is questioned about the failure of his previous film, The Lodger (1927) which was released five year earlier in 1927 and the actor made eight other films in that time frame. Novello's previous film in the story's chronology was The Phantom Fiend (1932), which was a sound remake of "The Lodger."
In an attempt to keep the dialogue in scenes feeling more natural, Robert Altman read the script as little as possible so he wouldn't know the characters' lines. He relied heavily on script supervisors to ensure that all the important beats in scenes were met, consulting with them after each take.
Robert Altman: [dialogue overlap] 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. He first developed this technique during A Wedding (1978) and used it several times.
The trivia item below may give away important plot points.
When Denton (Ryan Phillipe) is ravaging Mary Maceachran (Kelly MacDonald) in his room, Denton's vest rides up and there's a quick glimpse of two labels sewn on the waistband of his pants. One label says "Fox Film corporation" and the other says "wardrobe department." The camera focuses on these labels for a few seconds, clearly indicating to the viewers that Denton is not whom he seems.