I have an idea there were two incidents from Biggin, one was Cherokee, the other a Beagle Pup. Think it was the Cherokee that landed in a park and was later flown out by the CFI. Pilot was a disaffected club member, family problems or something?
Vague recollection is the Pup was landed on the unfinished M25 near Godstone/Oxted. Might have just been a forced landing though.