We found the stone with some difficulty as it is tucked away in some obscure shrubbery in a turning at the bottom of a long down hill road within the rather exclusive looking Bownham Park estate (which also contains Bownham House). The houses look relatively recent and I imagine the land in question once marked the boundary between Minchinhampston and Rodborough Commons.
A grey oolite (?) stone similar to the Long Stone at Minchinhampton though not holey. It is set in concrete with a curious 'step' at the bottom - can only speculate on its intended use. Stands about 2 metres high though on a slope so difficult to judge - it is just by the entrance to a detached house at the top of a small road containing other similar properties.
Horestone on Rodborough Common
@Thesweetcheat - we also walked to the curious milestone mentioned by D.P. Sullivan about a quarter of a mile away just across the road from Whitfields Tump long barrow. The indentations on one side are odd aren't they - look like they were made with a hammer and chisel but very neat and round.
I've submitted this to the TMA EDs as a new site (or possibly a disputed site) and, if accepted, will add clearer instructions on how to find it and some more photos.
Is the 'step' part of the same stone because if it is it looks quite deliberate doesn't it.
Roy