I can't help with whether or not it's actually accessible (or even there) but if I was walking the HWP I'd probably have a go at trying to find it. Looks like it's (potentially) only a couple of hundred metres south from the path in a field. A quick aerial view in Bing maps shows a patch of "pale" on what looks like a high point so it could be that (or the site of where it once was?). There doesn't seem to be a noticeable path leading to it from any direction though.
My only concern would be the farm(?) to the west of it as it's probably their land I would be about to trespass on!
Interestingly, Historic England doesn't seem to have that particular one listed as a researchable item yet it has it marked on their map, albeit in a slightly different location (to the west of the farm rather than the east).
Oooh, this sort of treasure hunting is right up my street