Think this one has been sorted.
I looked it up on Wiki-pedia. Heres the link
Heapey - Wikipedia, the free encyclopedia
Apparently BAE have a depot there that could be the same thing. If thats the case then it will be an explosives store. Explosives have to be stored in a remote, safe location (I used to have to inspect explosives stores) and that place would make an ideal location. For me, that's mystery solved. Obviosuly, its got to be secure so BAE arent going to let anyone just wander in to their explosives store, but il bet anything that thats what it is.