it may also be that one of their main attractions seems to be that they are used for filming, product launches etc and may be more sensitive than most. If they believed you may be covertly launching something without paying them then that may cause some friction. See here :

http://www.stonor.com/filming.htm

They can't stop members of the public photographing themselves, and probably don't care. I suspect they are sensitive to losing revenue for "corporate" events. You must have all looked very proffesional !

Paul