I asked a mate of mine - coincidentally an ex-RAAFie like me - who's been flying GA for decades in the UK, what airspace arrangements apply around fighter jet bases like RAF Coningsby. His reply says, among other things:
In UK there’s a concept called MATZ (MIL Air Traffic Zone). Technically they’re optional for us to avoid, but we “should” seek permission to enter. They’re treated as class G otherwise. This is the main form of protection for fighter bases in our busy airspace like at Coningsby. Some RAF stations have Class D around them, notably Brize Norton. That you can’t ignore but I’ve never had a problem asking for a crossing. Also in UK we have no designated Low Flying lanes for the fast jets: they can (and do) this any/everywhere. We all just have to see and avoid!
One wonders how the RAF can possibly survive and remain competent without thousands of cubic kilometres of restricted airspace to fly in.