I agree with you but honestly the question doesn't make sense and shouldn't have required this much effort put into answering it.

If it's a British or British and American production it's going to have people speaking with British accents. British actors speak with British accents. That's the common sense answer that people used to reply to Kyru99. Most films are made in the the language and accents of their producers and/or their main audience. With maybe the exception of Gladiator, the films he listed are not period films. If they were making a film about the painting of the Sistine Chapel with British actors, they wouldn't speak Italian. It's rare that people speak with accents unless it's germane to the story (immigrant, visitor, traveling, etc.)

If the question was about people affecting a British accents in a non-British setting with a non-British cast and crew to give a sense of "otherness" or to heighten its importance or something like that, I'm not seeing it. It might be there, but I've never noticed it.