Astonishing. Even being based in Lincolnshire, where every few fields there seems to be another former airfield, this overlay is a real eye-opener. For those seeing this on RLI/DII (which doesn't allow Google Earth), I strongly advise looking again at home.
Kind of makes you wonder how we got where we are today!
And as for spotter sites, try these two:
Sub Brit Project Rotor Sites
Sub Brit Home Page
STH