I was there for some TV filming about 8 years ago, and, as Buff mentioned, the airfield was closed, although it still had MoD Police on the gates and second entrance.
The TV company I was advising at the time were using the HAS's, and the Command Center, the latter a huge, purpose-built NBC equipped bunker, for use in time of war, most of which was underground, and had access for trucks, through very thick, blast proof doors, sunk into shafts between the 'floors'. It had been built at a cost of £13 million, just three years before the airfield closed!
At the time I was there, one of the 'Top Gear' programmes was being filmed also, out on the runway, and one of the 'super cars' being used ended up a wreck - something not shown in the TV show!