In a scene set on 1 September 1992, when Harry and Ron arrive at Hogwarts in their stolen flying Ford Anglia, and are being punished for their various offences in doing this, one such mentioned is that they were spotted by Muggles in various places -- including flying past the "Post Office Tower".

There are least two things wrong with the above:

1) In 1984 the former GPO (which handled all British communications) was split into two; mails and their infrastructure were handed to Royal Mail, while electronic communications and their infrastructure went to British Telecom. The correct name for the above building has thus (since 1984) been the "BT Tower".

2) and even worse, Harry and Ron were navigating to Hogsmeade by following the Hogwarts Express. All railway tracks (real and fictional) from King's Cross run northwards. So how on earth could they have passed anywhere near the BT Tower, which is about a mile east and half a mile south of King's Cross?