Continuity mistake: The last shot, when the camera pans away from the front door of the house, appears to be taken from a helicopter, and a modern 1990's white car can be seen parked behind the property in a courtyard. The shot was meant to be at the end of WW2. There's also a motorway in the background with lots of fast moving traffic.
Factual error: In the scene towards the end of the film where Stevens (Anthony Hopkins) is about to walk into the Hotel to meet Mrs Benn (Emma Thompson) for the last time a modern Nat West Bank sign is clearly visible for about three frames in the top right of the screen. The Nat West Bank did not exist in 1956, where this scene is supposed to take place. At that time it was still the National Provincial Bank and the Westminster Bank. They merged some years later.