I agree it has the right "style" of a proper standing stone.

BUT The thing that I noticed though was the fact that the piece of land it's standing on feels artificially 'raised' above the level of the road and other land around it. And not in a standing-on-top-of-something-else kind of way.
Imagine the trees aren't there. It doesn't strike me as being sited in part of a naturally-contoured hill, or a barrow-type mound either.

If I was to have to bet either way I'd say a really good folly, done by someone with taste and a nodding respect to the originals.

.o0O0o.