I think that you have shot yourself in the foot here because:
Let us say that I own a beautiful garden - we shall for arguments sake call it Kew Gardens, I would naturally expect large numbers of people wandering around admiring the flowers, and it would not matter to me whether or not they belonged to a camera club.
If it was my own garden at my present house, then I would be alarmed to find people wandering around it
without permission, because my house/garden is not open to the public.
The prime goal of a shopping centre is to attract as many people as possible, in order that they may spend as much money as possible. It does not take a businessman of the stature of Alan Sugar to work out, that less people will visit that shopping centre, if the staff appear overbearing, officious or aggressive.
I totally understand what the "rules" in this case are, so no need for you to bang your head against the wall, you will simply get a headache over nothing.

My problem is with the inconsistent application of those "rules", and more to the point the fact that the "rules" are pretty ridiculous by any stretch of the imagination.