Among London's many subterranean secrets, some of the most alluring are the concrete bunkers from the second world war and the cold war — and even those in use today.
The most famous is not a secret at all (although it was). In fact it is so not secret, it's a museum. The Churchill War Rooms under the Treasury was built in the late 1930s, and became operational as an underground government HQ just days before war broke out.
Housing regular War Cabinet meetings it was manned round-the-clock by service personnel who lived down there. Winston Churchill's office-cum-bedroom (which he rarely used) was luxurious compared to the facilities below the bunker in the section that's not open to the public (although we've been round it).
Although it was top secret until 1945, it only took a few years of peace before MPs called for it to open publicly.
For decades, visits were by appointment-only although by the 1970s the sheer number of requests led to calls for it to be turned into a museum. The Imperial War Museum took over, and the Cabinet War Rooms were opened to the public in 1984.
Whitehall, though, still has many bunkers that aren't open to the public — and we're not just talking about the out-of-bounds parts of the Cabinet War Rooms.
The modern equivalent goes by the code-name 'Pindar' and is located deep under the Ministry of Defence. It’'s been operational since the early 1990s, only coming to wider attention when the costs over-ran (mainly because of problems installing the computer equipment in the limited space).
Pindar is intended to serve as the main government HQ in the event of an emergency, although in such circumstances military operations would continue to be controlled from the Permanent Joint Headquarters at Northwood.
The bunker is said to be linked to Downing Street and the Cabinet Office via an underground tunnel, while the government has always denied rumours of it being connected to a tube station. It most certainly is not open to the public.
Elsewhere in the Whitehall area, the Admiralty’s Citadel is clearly visible above ground (described by Churchill as a "vast monstrosity", it's that concrete structure on the north-west corner of Horse Guards Parade). Built in 1940-41 and intended to be used as a fortress if German troops reached London, it was known as HMS St Vincent for years and is still used by the Ministry of Defence.
It’s believed to be linked by tunnel to other government buildings in the vicinity.
The tunnel network underneath Whitehall is variously known as QWHI, Post Office Scheme 2845, and Q-Whitehall. Constructed during the second world war, it's said to connect with the former Trafalgar Square tube station (now part of Charing Cross) while extending south to the Treasury (thus providing access to the Cabinet War Rooms) and beyond to Marsham Street where it linked with the government air raid shelters located under what had been a gas works.
Files on this site are classified and the tunnels are not open to the public, although back in 1980 journalist Duncan Campbell managed to gain access to the tunnels and found a (closed) entrance to Q-Whitehall near Trafalgar Square.
A number of tube stations have secret(ish) facilities attached to them. During the second world war, London Transport built eight deep-level air-raid shelters beneath Belsize Park, Camden Town, Chancery Lane, Clapham Common, Clapham North, Clapham South, Goodge Street and Stockwell (plans for a further two at St Paul’s and Oval never materialised).
Although they are all thought to have been initially used by the government (some of them as army barracks), five of them — Belsize Park, Camden Town, Clapham North, Clapham South and Stockwell — became public air-raid shelters when the Luftwaffe started attacking London with Doodlebugs and rockets in 1944.
The Chancery Lane shelter, accessible via unmarked doors on High Holborn, was designated as the Inter Services Research Bureau — a vague term which has led to all sorts of rumours about what it was used for.
In 1949 it was handed over to the Post Office and became the Kingsway Telephone Exchange, a secret communications facility that would be secure in the event of a nuclear war, and which for a time was used to connect the hotline between the White House and the Kremlin.
Abandoned in the 1980s, current owner, BT, put it on the market in 2008 (it still hasn't sold).
Elsewhere, the Goodge Street shelter was used by General Eisenhower and his staff. This one had two entrances — one on Chenies Street, the other next to the American International Church on Tottenham Court Road.
All over London adverts have appeared offering the shelters as underground storage spaces, and in 2015 we reported the shelter under Clapham Common is being used as an underground farm.
Fancy taking a look round one of these mysterious buildings? You're in luck — tickets to visit the shelter underneath Clapham South are available from the London Transport Museum.
Abandoned tube station
Another tube station that saw secret war service was Down Street, even though it closed in 1932. Located between Green Park and Hyde Park Corner on the Piccadilly line, it was developed as an underground bunker in 1939. Building work was problematic because the only available space was by the platforms and the Piccadilly line trains still passed the station, meaning work could only be done at night.
Down Street's principal wartime occupant was the Railway Executive Committee; the body responsible for the running of Britain's railways during the war, although Churchill also used it when renovations were carried out at the Cabinet War Rooms.
The Battle of Britain bunker
Secret bunkers are by no means limited to central London.
The RAF's No 11 Group —- responsible for the air defence of southern England in 1940 — had its HQ at the Uxbridge airbase.
Officially it used an old manor house within the base, but the nerve centre was the Group Operations Room in a nearby bunker. It was from there that the Battle of Britain was directed, and it was while leaving the bunker on 16 August 1940 that Churchill famously stated: "Never in the field of human conflict was so much owed, by so many, to so few."
RAF Uxbridge closed in 2010, although the Battle of Britain Bunker, which has been open to the public since the 1970s, continues to be run as a museum by the RAF, with the giant plotting-room map shown as it would have appeared at the battle’s height on 15 September 1940.
The idea of moving the government’s emergency HQ out to the suburbs in the event of Whitehall being heavily bombed was considered seriously enough for an alternative Cabinet War Room (codenamed Paddock) to be built underneath the Post Office Research Station in Dollis Hill in 1939.
It was rarely used (the War Cabinet met there twice) and was abandoned in 1944. The Post Office moved out in the 1970s, and the old research station has since been converted into a housing estate.
The local housing association is also responsible for the bunker, which is open to the public two or three times a year.
Here's a video looking round Dollis Hill:
Other government departments built emergency bunkers in north west London. In Cricklewood, the Admiralty built one underneath a nondescript building called the Admiralty Chart Establishment on the Edgware Road, just south of Staples Corner.
Known by the code-name IP (which reportedly stood for 'insurance policy'), it was completed in 1940 and used until 1944. The building above is currently derelict.
Meanwhile, the Air Ministry had a bunker in Harrow, underneath the Stationery Office. Station Z, as the bunker was called, opened for business in October 1940, and was apparently retained by the Air Ministry well into the 1950s, with the Home Office and Civil Defence also using the facility.
The site was bought by Kodak — which already had a large factory next door — in 1996. The photographic supplies company announced that its Harrow factory is to close and become housing, leaving things looking bleak for the bunker.
World war three
With nuclear annihilation a significant possibility during the Cold War, the government decided to move its underground HQ out of London — and to an RAF base in Wiltshire. The emergency plans for Britain in the event of a third world war saw London being designated as 'Region 5' with the local government being based in a large bunker at Kelvedon Hatch.
You can see a tour here:
In Cold War London, every local authority was required to have its own bunker, officially known as a Civil Defence Centre. These would have answered to five Group Control HQs (they had their own bunkers), which in turn would have reported to 'Region 5' HQ at Kelvedon Hatch.
Today, the best-known Group Control bunker is the one for south east London, and is located below Pear Tree House, an otherwise inconspicuous block of 1960s council flats in Gipsy Hill.
In the 1980s it was a focal point for local CND protests, and at one point Lambeth Council threatened to evict the London Fire and Civil Defence Authority from the bunker after declaring Lambeth to be a nuclear-free zone.
After the Cold War ended, the network of bunkers was surplus to requirements, and many were sold off although some councils retained theirs for use as storage areas.
Most of the Group Control bunkers no longer exist. According to Subterranea Britannica, there was one in Cheam that was demolished in the mid-1990s, while the one in Wanstead went the same way in 2000. Meanwhile, the one in Mill Hill was listed but nevertheless sold to developers and converted into luxury housing.
Additionally, a large number of pillboxes and public air raid shelters from the second world war still exist across London, some above ground and others buried below parks and various buildings.
The walls of these can be so thick that demolition has often been deemed to be more trouble than it's worth, and so they remain.