To prevent threats from insiders. For example, imagine one of her personal staff is blackmailed into placing a bomb in the Queen's handbag, or similar. Also, if

To prevent threats from insiders. For example, imagine one of her personal staff is blackmailed into placing a bomb in the Queen's handbag, or similar. Also, if she is flying commercially (the Royals use British Airways first class, I believe) then there is a legal requirement (Perhaps from the EU, or the CAA, and maybe also mandated by the destination's aviation authorities?) to search all passengers and X-ray their carry-on baggage, so she would not be able to exempted - remember flightcrew and even pilots have to go through screening!