Factual error: Toby joins the War Office, handles statistics for the RAF (an Air Ministry job) and then is suddenly said to be working for the Admiralty, but still in the same office in which he has been working since the beginning of the war. These were three completely separate ministries with separate buildings. Civil servants joined one or the other.
Factual error: In 1940, all the Americans are leaving London on transatlantic flights. Although the first commercial transatlantic flights began in 1939, they were suspended on the outbreak of war. Real commercial transatlantic service did not begin until after the war.