Updated at bottom:
A series of limestone caves deep under central London, which have been kept secret since their discovery in the 1950s are to be opened to the public it will be announced at a press conference later today.
The existence of the caverns under London was discovered in the 1950s during the digging of the GPO’s deep level telephone network under London which was designed to maintain telephone connections between the government and military in case of a nuclear attack.
Due to the sensitivity of the discovery, the caves were kept secret and two of the larger caverns were converted for use as a government command bunker, codenamed Huntigowk.
The command rooms are not hugely exciting – being a series of glorified portacabins stacked up inside the caverns and mounted on heavy springs to absorb any shockwaves from a nuclear strike. They were entirely about being functional and not really built for long term comfort.
The bunker was never put into use, but kept on standby while the much larger Burlington bunker was constructed near Bath. When it was decided that a central government command centre was actually quite a bad idea, the alternative plan for post-war government, Python was put into action on 1st April 1968, the central London bunker was decommissioned.
The whole area was still considered to be secret though, and it was only in July 2010, when the existence of Python was revealed that the additional details about the London bunker accidentally revealed the existence of the cave network.
Surveys of the caves began in 2012, initially just to work out what was down there and ensure it was structurally safe. However, it became quickly apparent that the caves could be a major tourist attraction, and a plan was developed to open them up to the public.
Although London is largely built on clay, which has long been a nice material to dig through, the bedrock underlying the clay is a natural limestone bed, and it was thought that the normally impermeable clay would have left the bedrock intact.
When the boreholes were drilled down in the 1950s by the GPO for its telephone tunnels, they suggested that contrary to original expectations, that the limestone would be solid, it has in fact a large number of caverns.
What was discovered is not just an unexpected series of caverns under London, but also a relic of the last Ice Age.
During the world’s most recent glaciation, what is known to geologists as the Anglian Stage represented the southernmost extent of the ice-sheet that once sat over the UK, reaching as far south as North London.
Before that ice sheet arrived, the River Thames didn’t flow through modern day London, but used to run north of London via Harlow and Chelmsford. The arrival of the ice sheet pushed the Ancestral Thames southward to its current course.
In addition to pushing the Thames southwards, the melt water from the ice sheet as it started to retreat some 420,000 years ago carved out the Finchely Gap – a long valley in the land leading down to the Thames.
At some point, and researchers are still trying to identify the location, it seems that the ice sheet melt water punched through, or wore away at the clay and gravels overlying London’s limestone bedrock, and started eroding away at the limestone.
London’s network of caverns were formed, then as the clay layer rebuilt up over the past few hundred thousand years, the caverns were lost once more.
There are 14 large caverns that have been surveyed are to be opened up to the public, and the two that were used for the cold-war bunker are likely to remain off-limits for a few years.
Not due to the secrecy, but because there are plans to convert them into a cold-war museum, similar to other examples at for example, York. It’s expected that the cold-war bunker museum will become a major attraction in its own right, and access to that could be separate from the main caverns.
The remaining twelve caverns will be opened up subject to funding being agreed to pay for the works needed to make the sites suitable for people to visit.
Access to the caves, which are deeper than the deepest tube tunnel will be via a series of lift shafts that will be drilled down to the largest cavern which sits underneath a section of Fleet Street.
At the base of the lifts, a large reception chamber will be dug out of the ground. The hoped for plan is to dig the chamber right at the boundary between the London clay and the Limestone bedrock to show off the boundary to visitors. The chief engineer of the newly formed Capital Caverns Company, Apru Chauntecleer, admitted that due to the engineering difficulties, it’s likely that the room will be lined with thick sheets of concrete to prevent the space being crushed by the soft clay above, and then a thin skin of clay and bedrock applied inside the walls to create the illusion of the boundary layer.
To create a dramatic entry to the caves themselves though, a bank of escalators will take people on the final stage right into the heart of the caverns. A series of walkways will then create a guided walk through the limestone caverns.
Several “rooms” will also be carved into the spaces, to provide the ever necessary “conference and party” revenues that the site will need to keep operating.
One of the more interesting uses being talked about is the trend for “outdoor” cinemas to be brought down to the caves. Having the advantage of not being ruined by the weather, the planners hope to be able to run film festivals all year around.
The full details are due to be announced later this year, and consultations will take place next April before planning permission is requested to open the caves to the public.
There will also be a competition to name the caverns, with the limitation being that they need to be named after London events or people — such as Dick Whittington, St Ēostre, Gog and Magog or St Pyrites of Ludgate. The details of the competition will be confirmed later.
The aim is to open the first of the caverns on 1st April 2020.
Yes, it’s that time of year again, and yes, it’s an April Fool. Sadly, there isn’t a network of caverns under central London… that we know of.
London’s bedrock is not limestone, but chalk. The 1950s deep level telecoms tunnels are nothing like deep enough to get to the bedrock, although some modern utility tunnels are now reaching those depths.
St Pyrites, is Iron Pyrite – also known as fools gold, while St Ēostre is a Germanic goddess associated with Easter, and a buried church.
The cold war bunker’s code name, Huntigowk is an archaic term for April Fool in Scotland.
The chief engineer’s name is also a clue: Apru (possible origin of April in Etruscan) Chauntecleer (the cock tricked by the fox in Chaucer’s The Canterbury Tales)
Today is also Geologists Day, so what better day to have an April Fool based around Geology.