The airports all make up the rules for themselfs, as long as they meet the DfT minimum requirements they can add anything they like.
The big problem is that they all have diferent local rules that a visiting pilot/engineer could not posably know about. This is were the friction starts has the heavy handed security ego kicks in and you find your self getting a dressing down from a numpty with an IQ lower than the dog next door.
In my opinion the DfT wants this situation to continue as this way if someting goes wrong they can blame the airport for not putting a local rule in place to prevent the problem.
Airport security is about two things.
First it is in place to prevent the DfT or goverment for getting any blame for an inccident (protection from the meda).
Second it is a way for the security industry to build an empire and make a lot of money by using a lot of low grade cheap staff and charging a lot for them.
Any security that we get from this system is totaly accidental.