It's only 'disused' if use of the site is uncontrolled and it's just lying festering away. Otherwise it's an inactive government aerodrome - i.e. it could be used, for example on military exercises or by ATC motorgliders.
Chivenor is listed as 'Strictly PPR (24 hours). Civilian aircraft not accepted'. What a shame - that's what you get when we hand decent aerodormes over to the grunts. Why the hell couldn't they have had Valley or Kinloss?
Brize should certainly have warned you about Abingdon. I will have speaks when I get back off leave.......