Done some investigating, and via one or two phone calls to different people and some asking about... one of the hangers is open again for the weekend (they had to shut some a while ago)
The place is a kinda overflow for the Science Museum from what I can suss out, and as such, there is some really really cool stuff, just without the poncey showing off, so those that like hunting through really cool gadgets/gizmos/old stuff/mechanical things etc should have a field day!
The hanger thats open will be the one that usually gets opened atm, has planes and aero engines mainly, with some vehicles. Fun things like the last printing press in Fleet St won't be on show though it seems.
EDIT: All info likely to have some kind of spin of some fashion... although most of it is from the place itself!