Found this easily yesterday, despite it always having put me off from even looking in the past - its on a wooded hillside right next to a dual cariageway road with nothing else nearby. But to my pleasant surprise, upon investigation (ie driving 75mph southwest along the opposite side carriageway) I saw there is an emergency phone and layby right in the right place on the northbound carriageway, so I turned round at next junction and went back. From the layby, hop over a little fence and follow a well worn path to the left for about 100 metres, and there it is !
Brilliant, its like the layby is deliberately put there for us stonehunters ! Pictures and description to come when I have returned from weekend at my sisters.
Something is not right. This message is just to keep things from messing up down the road