We found it!

Thanks everyone who offered advice

The 19th century granite column is situated in the grounds of Stanley Park which was the home of the Marling family from 1850-1952. The buildings were then converted to flats. You can just see the top of the column as you travel along the Ebley by-pass.

It is reported in a book "The Follies of Gloucestershire" by Headley, Gwyn & Wim Meulenkamp which you can see at http://www.touchwoodbooks.co.nz/tfollies.html . The book only says " ... and below Selsley, southwest of Stroud, is an Ionic column on a plinth standing anonymously in a field under the fantastic Stanley Park."

I have also been sent a photo of the monster...but its not ancient so you can't see it!

happy as a pig

Mr H