Factual error: It's Christmas Eve 1925. Tommy and his son leave a mince pie for 'Santa and Rudolph', but there was no reindeer called Rudolph until the 1930s. The character's author hadn't even graduated by 1925, and only began writing a book about a red-nosed reindeer in 1939.
Factual error: Kenya tea chests are marked KTDA. (Kenya Tea Development Agency). This did not come into being until the early 1970's.
Factual error: Jessie Eden is described as a shop steward. A shop steward is the senior part-time trade union official in a particular workshop or department, who also has an ordinary job in that shop. Jessie appears to be a full-time official and covers a number of factories. She would actually be referred to as a trade union organiser.
Continuity mistake: Tea leaves are visible to the top of the cup during the reading's close-ups, but the cup is clean each time the view switches to full screen. (00:29:30)
Factual error: The British Army had no female soldiers in the mid-1920s. Queen Mary's Army Auxiliary Corps was disbanded in 1921 and no women served in the army from then until the formation of the Auxiliary Territorial Service in 1938.
Visible crew/equipment: An iPhone being held by someone is visible through a window in the top left of the screen during the decoy vehicle scene near the beginning of the episode.
The Company - S4-E6
Factual error: Tommy makes a call during the episode to the USA, there was no system for international calls in 1926 for the general public, that was only introduced in 1927. (00:33:30)
Factual error: Arthur is "deputy vice-president" of the Shelby Company Ltd. This is an American position title that would never, ever have been used in 1920s Britain.
Character mistake: Ada is listed on the portraits of The Company officers as Mrs Ada Shelby. She is actually Mrs Ada Thorne.
Factual error: Lord Stamfordham has a paper before him headed 'London Constabulary Police'. There was no such thing.