Episode #9.1 - S9-E1
Continuity mistake: It is revealed in series 9 that Eddie Dawson is turning 70 years of age at the end of that year, however during the previous series which was only 1 year earlier it is mentioned that Eddie is 66 years old.
Character mistake: Joyce announces to Monty that she is getting married by "the only other person she kissed in the last ten years" (meaning Sir Henry from the consulate). However, that's wrong because she kisses Cyril Babcock on the beach in an episode of Series 6.