Boom mic visible: A boom mike is clearly visible in the top right-hand corner of the screen for several seconds (until the camera moves down to compensate) when Basil is talking about swimming to France.
Continuity: The psychiatrist's wife goes to have a bath. Later, she is seen in her room, but in another scene taking place a few minutes later, she is seen returning from her bath. Furthermore, her husband goes to have a bath during the time in which she is supposedly in there.
Errors made by characters (possibly deliberate errors by the filmmakers): When Mr. Johnson picks up the phone at the front desk, he accidentally rings the bell with the side of his hand. (However, Prunella Scales quickly stops the bell from ringing and continues with her next line as if it's no big deal.)