Factual error: In Blackadder's Christmas Carol, during the Elizabethan part of the 1988 Christmas special, Queen Elizabeth asks Edmund if he has any last words before she chops off his head and sticks it on the Christmas tree. Christmas trees weren't introduced to England until Prince Albert (husband of Queen Victoria) brought it from his homeland in 1840.
Audio problem: "Blackadder Back and Fourth": Blackadder and his guests are going to the cellar where the time machine is kept. While they are going down the stairs, Blackadder says, "To his exact specifications." However, his mouth is shut and his lips don't move. (00:03:35)
Continuity mistake: "Blackadder Back and Fourth": Blackadder and his guests are going down stairs. Blackadder is first, George is second, Melchett is third, Elizabeth is fourth and Darling is fifth. Blackadder gives his notebook to George. When they arrive downstairs, Melchett and Elizabeth are ahead of George. This is not logical, since the stairs are too narrow and they could not have passed George. (00:03:40)