Episode #3.2 - S3-E2
Factual error: Patrick Jarvis mentions Tbilisi. Nobody in Britain would have called the city by that name in 1924; it was still always referred to as Tiflis.
Episode #3.2 - S3-E2
Factual error: Father Hughes says that Admiral Hall may be detained in the House of Lords. Admiral Hall, although knighted, was never ennobled and thus did not sit in the House of Lords.