MPP quote; "so we also think it is very likely that the bluestones originally formed a rather different type of monument from a stone circle."

Two things; A Neolithic tomb, passage cairn, was found (buried) near to Carn Meyn in 2011, so presumably this is what MPP is referring to, he wants to find another near to one of his quarry sites ...

http://www.bbc.co.uk/news/uk-14733535

The other thing is of course the enigmatic 'horseshoe' monument of stones called 'Bedd Arthur' that lies about a couple of kilometres away from Carn Meyn...

http://www.themodernantiquarian.com/post/137965/bedd_arthur.html