Episode #1.7 - S1-E7
Factual error: Lorna uses the word 'okay'. The first recorded usage of this word in America was not until 1839 and in Britain not until the 20th century. The series is set in 1814 and generally uses language contemporary to its setting.
Episode #1.8 - S1-E8
Factual error: Sir Stuart Strange, on learning that Wilton and Pettifer have not been contacted conjectures, "they must have left early for the weekend" This was 1814 and the earliest recorded use of the word, and concept of weekend was in 1879.