In the mid 1950s, the threat of atomic attack by the Soviet Union was taken very seriously by the British government. The Royal Observers Corps were given the job, if an attack took place, of reporting nuclear bomb explosions and of monitoring radioactive fallout. Three men at a time crewed the post.
1,563 underground posts were built all over the UK for the ROC, and many still exist. This one is somewhere between Winslow and Aylesbury. I’ll not be more precise, as these posts tend to get vandalised or the contents are stolen. This post closed in 1991.
There are a few restored posts. Here is one, with a cutaway diagram of the post.
The posts were built to a standard design, although the hatch at the top of the shaft isn't always hinged on the same side, and some were built 'handed'. That is, to a mirror image plan. I have no idea why; can anybody enlighten me?
If you want to know more, there are at least two books on the subject. They are Cold War Secret Nuclear Bunkers by Nick McCamley, and Cold War - Building for Nuclear Confrontation 1946-1989 by Wayne D. Cocroft and Roger J. C. Thomas.
Anyway, here’s some photos I took last year.
Battery set switch. In the event of a nuclear strike, it is very likely that mains electricity would be lost. The battery (kept charged up by the mains until needed) would allow the crew to see what they were doing.