In the introductory voice over, schizophrenia is likened to multiple personality disorder (or dissociative identity disorder). In reality, these are two entirely different ailments, one being a disruption in a person's perception of reality (schizophrenia) and the other a disconnect between more than one personality state (DID).
Early in the film a man is reading a newspaper. At the top of the newspaper it says Thursday, April 29, 1974. In fact, April 29, 1974 was a Monday.
At around 1h 24 mins, a crew member can briefly be seen in one of the mirrors as Samantha enters the bathroom looking for William Haskin.
The first establishing shot, vaguely captioned North East England doesn't make any sense when paired with the next establishing shot. The first is of the Transporter Bridge on the River Tees, the next - suggesting Haskin lives in Newcastle - is the Swing Bridge on the River Tyne, about 40 miles away.