INFORMATION:

Foreground : is an EWS (emergency water supply) all around Charmy Down there are many EWS's.
Background : pillbox.
Below: picket screw in the hedgerow part of the barbed wire entanglement that would have been around its perimeter.

History: For a short time 137 Sqn with Westland Whirlwinds

a not a very successful plane.