Secret subterranean Britain mapped for the first time: New documents reveal the labyrinth of tunnels hidden under UK's streets

An atom-bomb-proof telephone exchange deep underneath High Holborn: The Kingsway telephone exchange was built as a deep-level shelter underneath Chancery Lane tube station in the early 1940s for use as an air raid shelter. But like many deep level shelters it was not used for its intended purpose and was instead used as a government communications centre. Material from the Public Records Office was stored there from 1945 to 1949 and the site was given to the General Post Office (GPO) in 1949. At the time, the Post Office was also responsible for telephones as well as postal system. The two-tunnel shelter was extended by the addition of four tunnels at right-angles to the originals. This extension was completed by 1954, and in 1956 it became the UK termination point for TAT-1, the first transatlantic telephone cable. Throughout the 1960s, 1970s and early 1980s, Kingsway Trunk Switching Centre (as it became known) was a trunk switching centre and repeater station with Post Office engineering staff totalling over 200 at its peak and boasted a staff restaurant, tea bar, games room and licensed bar. Its bar claimed to be the deepest in the United Kingdom, located approximately 200 feet below street level

The Post Office (now BT) network of deep level cable tunnels under central London. Most were built to give protection against A bombs during the 1950s. The Kingsway Exchange is pictured centre. The site, like others in the network, contained an well and rations to maintain several hundred people for months, ensuring a safe environment in case of nuclear attack

Planning for a deep network of Whitehall tunnels and War Rooms began before the Second World War. Each service ministry, the Cabinet War HQ and other civil and military administrators had protected accommodation in the 'citadels'. A deep level tunnel and lift shafts linked each citadel. The Cabinet War Rooms contains four main rooms - Churchill's bedroom and study, the telephone room, the Map Room and the Cabinet Room. The Cabinet Room was where Churchill and the top generals, admirals and wing commanders would have robust discussions about the direction of the war From 1950-53, new bunkers were built under Whitehall.

Map Room Officers at work in the Cabinet War Rooms. The Royal Air Force officer sitting at the end of the table is Wing Commander John Heagerty, and the picture is believed to have been taken in 1942

The Map room in the War rooms at Storey's Gate, used for military planning and strategy during the Second World War

Land registry map, showing the Anchor Exchange Birmingham in pink (1959). The  Anchor was an underground telephone exchange and nuclear bunker built in 1953 under the guise of building an underground railway and opened in September 1957 at a cost of £4 million. It was located on Newhall Street but its network of tunnels extended from at least the Jewellery Quarter to Southside. Code-named Anchor after Birmingham’s jewellery hallmark, it remains as a largely unknown and forgotten part of the city’s Cold War heritage. There are a number of entrances to the tunnels across the city, but these are still kept secret

The above image is a map of the underground Manchester Guardian telephone exchange, built in 1954. It was built together with the Anchor Exchange in Birmingham and the Kingsway exchange in London – all believed to provide hardened communications in the event of nuclear war. Today the underground site is used for telephone cabling. Hidden Manchester reports that the site was classified under a ‘D Notice’ in the fifties to prevent the media from writing about it. It was declassified in 1968, but those with knowledge of the site were still having to sign the Official Secrets Act in the 1970s