This, I believe, is Abenhall (or Abinghall) House sold by auction in 1867, as mentioned in Mike Pinchin's post. It is not at Gun Mills but a mile or so north near the A4136.

http://www.geograph.org.uk/photo/3347192

I have in my possession an indenture of mortgage made 23 October 1895 between Philip Nicholls, collier (my great grandfather), and John Robinson, solicitor, of Abinghall in the County of Gloucester.