Thanks for all the responses, I understand the restrictions on active bases, though the Hawkinge museum is in the middle of a rather souless housing estate! Having said that, I've taken photos (with permission) inside Luggershall, Ashchurch and the D&M school at Bovington, the only concern was that the photos did not give the positions of the buildings, a concern rather negated in recent years by Google Earth!
I recall the RAF Museum at Hendon had a "no flash" rule at one point, though that was apparently because flashes were triggering the fire alarm, but photography was still permitted. I'm not convinced by the 'flashes cause damage' excuse, possibly if the flashes were constantly repeated over a period and the same museums often leave stuff outside to fade anyway.
Some museums feel there is a "copyright" issue, but as far as I am aware that is just one interpretation of the current law, and unproven in court.
What seems petty and pointless is the ban on note books.
By the way virtually all the exhibits at Hawkinge are replicas anyway.
jch