"What stands out in Britain BC is the lack of megalithic stuff and him shoehorning his 'realms' theory onto the Stonehenge landscape. If he had chosen a 'simpler' site he probably could have been much more convincing".

It's not just Pryor's theory. Parker Pearson & Ramilisonia wrote a nice paper on the subject which was published in Antiquity 1998.
Drop me an e-mail and I'll scan you a copy.