Royal Observer Corps Monitoring Post

I've probably driven by this hundreds of times but didn't notice it and wouldn't have known what it was either.

Thanks to a quick drizzly geocaching trip I now do :) 

From geocaching.com:

'Royal Observer Corps Monitoring Posts are underground structures all over the United Kingdom, constructed as a result of the Corps' nuclear reporting role and operated by volunteers during the cold war between 1955 and 1991.
In all but a very few instances the posts were built to a standard design consisting of a 14-foot-deep access shaft, a toilet/store and a monitoring room. Almost half of the total number of posts were closed in 1968 during a reorganisation and major contraction of the ROC. Several others closed over the next 40 years as a result of structural difficulties i.e. persistent flooding, or regular vandalism. The remainder of the posts were closed in 1991 when the majority of the ROC was stood down following the break-up of the Communist Bloc. Many have been demolished or adapted to other uses but the majority still exist, although in a derelict condition. This one appears to be well maintained, and is listed under Fordham. It opened 1.4.1961 and closed 1.9.1991. we have been unable to find out any more of its history. Is it possible it is still in use?
The vents and hatch to the underground monitoring post are within the enclosure, with a visual reporting post beyond.  Part of the ROC's role was to report the extent of nuclear fallout.'