Fairoaks. Clapham Junction to Woking non stop in under 20 minutes then 3.5 miles to Fairoaks (bring your bike or a short cab ride, no public transport).
I reckon that's one of the easier ones to get to with a choice of
London Transport Flying Club or
Synergy Aviation
The airfield doesn't have the "buzz" of Denham or White Waltham but from Clapham Junction without a car, it's probably the most convenient to get to.