Throughout all three series the numerous files and folders being handled are all headed "Ministry of Administrative Affairs" even though the setting is the Department of Administrative Affairs.
During the train sequence in "The Official Visit", a close-up shows that the warning notice on the wall is written in gibberish.
Televisions come on instantly, which didn't happen at the time the series was made.
Bernard will often answer the telephone, listen for a second or two, then deliver a lengthy message of what he was supposed to have heard.