Saul, without wishing to offend you, I don't thing civilians should be allowed to attend the gyms at MOD bases. I always understood it as a perk of being within the service, and also an actual real facility used to keep service people fit (fighting fit, fit for service life etc). Without others getting in the way, holding up others in the queue. Once your out of the mob, you should be out-think that's important point to mark out and this is one way of doing it.
That sounds terribly rude I know. I'm now a civvy, don't work for MOD or contractor so yes maybe I would say this.
Also, for vetting reasons/humanitarian reasons/all sorts of reasons you don't want crusty letching old sweaty civvies training alongside u18 trainees etc. because it makes the kids uncomfortable and probably breaks the little darlings human rights (true dit).
Ex navy using the facilities got on my nerves a bit at the tail end of my time.
I used the Nuffield gym as a civilian and it was very reasonable on cost and very good on facility.