Fairlop (ex Spitfire base), East London, runways gone for hardcore and then totally obliterated by years of gravel extraction. I was brought up on the other side of the Central Line and well remember playing amongst the tank traps and pill boxes in the 50's....
Witney, Oxon. Possible to trace the the layout via the industrial estate. Visiting the JR hospital recently and met an old lady who worked in the de Havilland repair shop during the war. She had some nice tales to tell!
Harrington, near Sywell, is a more traceable site with an impressive covert history from the US Carpetbaggers operations (RAF Tempsford nearby was the UK equivalent) to the Thor missile site operations of the Cold War. Google Earth shows the remains of the missile launch platforms. The museums there are both well worth a visit. See
http://harringtonmuseum.org.uk/Location.htm
There's a small memorial to a wartime Spit pilot who dropped in for lunch and the chocolate that the Americans had, put on "a show" for the Yanks and departed low and barrel rolled it into the Admin hut. Also parked outside is a blue T6 that seems to have been abandoned by it's owner (visible on Google, the Harvard, not the owner...)
Nothing much left of Twinwood Farm north of Bedford now. I landed there years ago as part of my gliding Silver C. Runways totally gone, but the peri track shows where it was, now just a ghost in the fields. That's where Glen Miller took off from on his last, fatal flight.
Hope this interests
Ripline