Episode #3.6 - S3-E6
Factual error: Tommy says that the Chief Constable of Birmingham has issued a warrant for the arrest of Arthur, John, Polly and Michael. Only a magistrate or judge can issue an arrest warrant. The senior officers of the Metropolitan Police were sworn in as magistrates, but not those of other forces.
Episode #3.6 - S3-E6
Factual error: The locomotive used to pull the train is a LMS Black 5. This class of locomotive was not built until 1934, 10 years after the year this episode is set in. (00:32:25 - 00:32:55)