As far as viable and currently serviceable airfields go, Wittering could fit the bill.
Operation: Class G airspace, big currently serviceable runway, and airfield site including ATC. Reasonably centrally places for visiting aircraft. Downside, A1M crosses eastern undershoot.
Public
asy access via A1/A14. Plenty of space for on site parking at the western end. Stamford close by for rail/bus link.
Would RAF allow site use? Dunno.