Errors in geography: The story is supposedly set in Suffolk, where you simply would not find the wild heather-covered moorland of the location shots on the Isle of Man.
Continuity: When Simon is drinking his tea in the first shot, he receives the cup with his right hand and then turns the handle to actually drink with his left. The handle switches back and forth in subsequent shots.
Anachronisms: Rose sends Cassandra a bottle of what appears to be Penhaligon's Bluebell perfume for her 18th birthday. According to the Penhaligon's website, the Bluebell perfume was first manufactured in 1978, whereas the film takes place around the early 1940s.