Hidden away underneath a particularly nondescript brick building in the suburbs of North London – Dollis Hill to be exact – lie the standby cabinet war rooms. These bombproof rooms would have been put into use for Churchill’s cabinet should the secret war rooms in Westminster have been damaged or destroyed. Thanks to Subterranea Britannica, the rooms are opened up a couple of times a year, providing you with an opportunity to explore their beautiful dereliction.

Plans for the standby cabinet rooms began in 1938, with war imminent, and construction commenced in 1939 below the site of the Post Office Research Station. After 13 months and at a cost of £250,000 the rooms – code-named ‘PADDOCK’ – were complete. As it turned out, they were only used for cabinet meetings on two occasions, with the more vulnerable Westminster rooms remaining unharmed. After the war the entire site reverted to use by the Post Office. They moved out in 1976 and the war rooms have been unoccupied since. Houses were developed across the site in the late 1990s, but on the agreement that the alternative war rooms remain and are opened up to the public at least twice a year.

As these photographs amply attest, the rooms’ original features are still in situ and in a high level of dereliction, with stalactites forming on the ceilings, fittings rusting away and mould blooming on walls. Our tour included the air filtration room, the lower plant room with its massive generator, the telephone exchange room and what was once the map room, which would once have had maps adorning the wall and a map table in the middle of the room. Today the maps have disappeared but you can see the tide mark from the water that had flooded the map room after it was abandoned. What we didn’t visit was the toilets, as these were amazingly left out of the design process – apparently a fire bucket or a dash to the post office buildings above had to suffice.

Last weekend’s opening was part of the London Festival of Archaeology, but the site will also be open for tours again in September as part of Open House London, and I highly recommend adding it to your list for that busy weekend.

Subterranea Britannica also has detailed information about the rooms on its website.