PhilD Strickly legally speaking, I have no doubt that you are perfectly correct.
However, when faced with the security staff at say, Norwich, who demand an ID, with a photo on it, BEFORE that will let you out onto the apron, producing a passport, seems to be the quickest solution.
At many regional airports, GA pilots have to walk past commercial aircraft to get to the little'uns. So presumably the airport security staff owe a duty of care to the commercial passengers, not to let just anyone onto the apron, without checking who they are first.
Whatever the ANO may say, this is just the post Sept 11th realities.