47 UK airfields, 96 in total. I'm sure there are plenty of folks with close to 500.
My "Airfields List" shows as "open and operational" in the UK:
132 licenced, open to GA,
50 military, open to GA
19 "unlicensed" but open
11 licenced but GA banned or restricted (like Heathrow)
7 military where GA is not allowed
11 unlicensed with restrictions on GA
510 private strips which may or may not be open (and there are probably lots more I don't know about)
86 gliding sites (some accept GA, some don't)
82 helicopter sites
67 microlight sites.
So that's 975 "possibles" depending what you fly. There are certainly many more fields used for occasional aircraft visits, so the sky's the limit.
The sad part is that there are 2,285 in the "is or was an airfield" list, so we've lost more than half of them, and there are only 132 now useable for flying training. Many of those are under threat. Hence the efforts of A4A - see
http://www.airfields.org.uk/