Yes. In 2005 when we held the NAMHO conference in Surrey we tried to arrange a trip to Brightling. Although initial enquiries looked promising, eventually it transpired that visits would only be entertained for British Gypsum clients. We declined to set up a contract with them to provide us with a large stack of unwanted plasterboard panels, so the trip had to be dropped from the schedule. Mountfield is also BG.
As for giving a talk - sorry, I don't have any contacts I can think of.