Factual error: 2-7 "The Crimsom Avenger": At Dunwyn Erwyllan grabs a bundle of money bills from a fishmonger. It may be just a curiosity since paper money wasn't used in real medevial times, but it is still odd as gold coins are still in heavy use in all other episodes. Even the royal treasury, which is robbed in this very episode, has only bags of coins and no bundles of paper money.
Song of the Younger World - S2-E20
Factual error: The 19th Century reformatory has modern electric light bulbs hanging from the corridor ceilings. (00:21:10)