CS,
The location in your photo seems very familiar. The reason I suggested HMS Dryad, is that some 15 years ago I was on a Maritime Ops acquaint course at Dryad, but not the main site. It was at a large house in the same area. At least, I recall leaving the motorway at the Boarhunt junction and then following narrow lanes to the location, in a very quiet valley. I'll try to joggle the remaining brain cells to see if I can recall any more info.