There is an interesting article in The Sun that says amongst other things, that Harry is asking lots of questions about Diana's death e.g. " Official judicial sources in Paris say the Duke of Sussex’s researchers have been seeking information about the car crash that killed his mother 25 years ago." One of the questions is allegedly whether Diana had been offered security after her divorce.
After her fatal crash Scotland Yard asked why Diana had no security. Tina Brown said that Diana had turned down security. But the suspicion is that Diana is in the same situation as Harry i.e. only offered security if attending an official royal event such as the Jubilee, but refused security for the rest of the time.
I know it is The Sun, but given Harry's fight around official security in the UK, which he has offered to pay for but still been refused - it rings true that he would be asking questions about his mother's security. It is clear if she was using official security at the time, she would still be alive.
www.thesun.co.uk/fabulous/19503595/prince-harry-diana-final-moments-book/