Nor does Northumberland, but we've a few big hills in the Cheviots with BA burial cairns on top of them, most of which have been trashed at some point. Shillhope Law and Windy Gyle are good examples of how a BA cairn has been mucked about with for centuries. Neither of these have a walkers cairn on top of the actual burial cairn, but rather just to one side, which is fairly typical of the area. Instead, the burial cairns have been re-jigged to form sangars forbeacon watching folks as late as the Napoleonic wars, possibly from as early as the romano british kingdom of Byrnaich. Then the nice OS people plonked a trig point there. Which is no coincidence really, as most of the hills that were chosen to be adorned with burial cairns just happen to have extensive views, at least as far as the next big hill with a cairn on. other places I've seen the ramparts of hillforts piled up as 'modern' walkers cairns. In both situations, it was obvious that there was prehistoric remains still in situ, as there'd be turf-fast bits of cobbles spread over a wider footprint, which would be quite easily distinguishable from the surrounding terrain by dint of the increased concentration of buried stone when compared to the immediate vicinity.

So, what I'm getting at, it that though a walker's cairn isn't evidence of diddly-squit, in conjunction with other factors such as viewshed and intervisibility with other monuments, it might be possible to claim that some walker's cairns are the re-arranged remnants of prehistoric monuments, but I'd be looking at the footprint of the cairn and the amount of stone naturally lying around.

There. I've discussed. I really should go find a photo of Shillhope, I'm sure I've one that clearly shows the kerb of the original cairn, the beacon sangar, the trig point and the walkers cairn.

Neither does Scotland , lots of hills though .