Hello Philip,
From my own experience, and bearing in mind your nephew's age, I would say that it's perfectly natural for him to feel depressed, particularly concerning the reason for his mother's death. Two years is nothing in such circumstances. Consequently I don't agree with his previous GP's decision to prescribe anti-depressants although they typically do. Drugs don't address the underlying cause, they just mask the symptoms as I'm sure you know Philip.
macafee2's suggestion is a better solution. Ideally, your nephew may benefit from talking about his feelings with someone who has had the same experience, or a psychologist, but steer clear of psychiatry and drugs.
I hope he manages to resolve the medical records problem. As you know, the NHS' bureaucracy can be very demanding.
Simon