Grey GPO object ( with adornment )
The road on which it is located has no overhead telephone cables, so I assume that they are buried and this may be a cable marker.
But it looks like it has a lock suitable for a utility key, which would suggest that it opens or that the sleeve slides-off.
There are no other examples along the road, and this one is tucked-in under a hedge.
Goscomb ( BE Wholesale ), Exchange NINTS