Mmmmm. I began to ponder whether or not the Grebe was in front-line service as late as 1930 (one has to do something crawling behind a lorry at 20mph on the A420). And it wasn't. Neither 19 nor 29 were flying the Grebe in 1930, according to Jeff Jefford's RAF Squadrons - they'd moved on to Siskins by then. On top of that, the badge in the photo looks a little like 25 Squadron's. Very odd, until...
Digging out Thetford's Aircraft of the RAF Since 1918, it transpires that J7530 was a Grebe IIIDC, a two-seat dual control trainer. I quote:
"Six of these were flown by No 25 Squadron (J7520, J7530, J7532, J7534, J7536 and J7538) to assist the training of pilots in the skills of formation aerobatics"
So we know the type, but we're now left with the awkward fact that 25 Sqn was also Grebe-less by 1930. Either 25 kept the trainers on charge to continue formation aerobatic practice, or they moved to another unit. And in the photo, the aircraft is lacking 25 Sqn markings (the silver/black bars).
So, where next? Well, another book later, and it appears that the Coastal Defence Co-operation flight was at Eastchurch in 1930, as was the armament and gunnery school. The badge on the tail might be for one of those, perhaps.
It seems, therefore, that as long as the date of loss is correct, the aircraft almost certainly wasn't 19 Squadron's, was possibly with 25 and could well have been with a second-line unit at Eastchurch.
And the photos are splendid, Adrian. They're the sort of thing that get lost very easily over the years, (when they ought to be preserved for posterity), and no-one gets to view them - so please keep posting them!