I suspect we are going to discover that this land is not adopted and is in fact owned by the property management company that owns the freehold of the site - the 10 different companies then either lease or rent the premises from the landlord.
The access land then of the type that Ethel mentions quite a lot in relationship to traffic violations - because the land has public access, some RT Acts apply to it, but the freehoildder has the right to constrain the vehicles that park on it.
So, yes, it can be subject to clamping.