When Henry calls Libby to tell her Daphne has been out all day with a boy in a band (Ian), Libby says, Lemme guess, he's a drummer? In reality, Oliver James, who plays Ian, is a drummer.
Anna Chancellor and Christina Cole who play mother and daughter in this movie both played Caroline Bingley. Anna in Pride and Prejudice (1995) with Colin Firth (who is also in this movie) and Christina in Lost in Austen (2008).
When Armistead and Daphne are on the dock at the party, right before Daphne pushes him into the water, Armistead starts rubbing Daphne's arm with his right hand. But in the shots from behind Daphne, it's obvious that Armistead is only miming the action and rubbing his hands in midair.
When Daphine is riding in the number 8 bus in London it says "Trafalger Square" in the front. The actual number 8 bus does not stop at or near Trafalgar Square.
When Daphne is spotted through the window by Clarissa she runs away from the house and is met from the opposite direction by Henry who was in the house when she ran away.