Visited a couple of years ago and must admit I don't recall the stones... however (according to my fieldnotes) I had a long chat with the farmer and he seemed pretty clued up about the site and what it represented.... hard to believe a chap with that awareness would dump field clearance on the barrow? Then again.
Well this is it, they looked 'new', they didn't look like they'd been dug out of anywhere from their colour. The field is apparently set-aside at the moment so I don't know why they'd be clearing big stones from it. Last time I went (admittedly years ago) I remember horses in the field grazing, it didn't have crops in it, but maybe it has had in the meantime and that's the thing. Maybe that's all it was, field clearance, or maybe even they're stones from the barrow long taken out and now 'refound'. They were big-ish you see. Dunno. If you are passing, Scubi, do have a look?
Well just visited the site and I am convinced the stones are not from the barrow as there is no recent excavation and the remaining exposed chambers are all present and correct.
They are very similar size and type to those used for the chambers (I am no geologist so I am making assumptions here) and I think they have been there a little while as there are no track marks leading to them, but not long enough to embed themselves into the soil yet either.
There are about a dozen in all and like you said Rhiannon they are vary clean with very little sign of soil staining. A few have lichen/moss on their upper surfaces where the rest do not maybe suggesting they could have been stacked up somewhere for a time and the moss only grew on the exposed surfaces.
I couldn’t see any indication of extraction in that or some of the adjacent. Possibly they have just been dumped here because they were in the way.
I was hoping to see a farmer to ask but no such luck for a change.
Maybe somebody intends to reconstruct the barrow……well maybe not then!