Thanks guys for the helpful replies. The aircraft in question is definitely not dropping parachutists; through my binoculars it's just a normal 2 seater with non retractable undercarriage and a noisy prop! It's possible he could be using another airstrip a few miles further NE according to a neighbour, so until I can eyeball him taking off there's not much I can do. I'll do some more detective work and let you guys know the outcome.
bose-x, unable to PM you as your mail box is full!