An underground post with the counter balance weights on the exterior of the hatch cover.
Thoughts so far...
...I was sure it was the post at 8/K2 Cotgrave, decommissioned in 1968. This proved not to be the case !.
...must be Sherburn Hill, Co. Durhan. But again, on visiting Sherburn Hill a couple of months ago - nothing now remains apart from two ' suspect' grass covered mounds, again, it cannot have been this post either. Why ?, because in the photo, there's clearly a stone wall in the background, and neither of these sites has a wall within miles !.
...Answers on an email! to Geoff Cameron firstname.lastname@example.org