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 the 1950s. 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.
Factual error: At the end of the film, the bus in 'Clevedon' (in reality filmed in the nearby town of Weston-super-Mare) has destination boards that are actually localities in Exeter which is about 60 miles away, the type of bus and specificity of the localities, and the fact this was very much a local bus service and not a long distance coach probably mean the bus was from a collection in the Exeter area and no-one bothered to change it.