After three site visits for discovery, better photos and habitat checking, and numerous emails with David Manning we have settled on this being Grapholita pallifrontana, a UK BAP Priority Species. Confirmation was hampered by the photographs showing a characteristic that Bradley said was diagnostic of a very similar species G. internana. That species feeds on gorse, of which there is none on site (one of the visits was to check this) whereas G. pallifrontana feeds on wild liquorice, of which there is quite a bit. These photos are of one sitting on a bramble leaf alongside a liquorice patch. Another adult was also present there.
When approached too closely the moth does a weird rotational dance, following by a random run around the leaf, then either runs underneath or flies off! For a close look it's necessary to first back off a bit when it starts girating, then, once it's calmed down, move in slowly.
It's worth checking anywhere that has liquorice for this species.