Hi POBJOY and Kenley RAF
Thanks for info re ack ack in Burntwood Lane as we went scrumping in disused orchard 100 yards away.
Regarding that remote square tallish building under tree canopy with no visible doors or windows below may give its location on South East part of air field.
Looking on Google satellite map run on runway from Wattenden end towards Whyteleafe Hill, pass 615 Gliders building on your right, continue into a grassed area and turn right say 2 o'clock (from run way direction) or 4 o'clock on map and walk 100 yards and under those trees was this square building.
Have a great trip and no doubt you will have a feed at the Wattenden and read stuff on the walls and owner may have more memorabilia stashed away in loft. Worth an ask. Cheers NS