Revealing mistake: On the episode where Diana goes to New York and visits the hospital, it is filmed in the Reynolds Building at UMIST. Visible through the window is the Mancunian way with the car travelling on the left (not right) side of the road.
Factual error: Sir Martin Charteris, depicted as being Private Secretary throughout the series (which begins in 1979), actually retired in 1977. Sir Philip Moore and Sir William Heseltine were the real Private Secretaries during this period.