In the event of a nuclear war the London Bunker, 125 feet (7.62m) below ground, would have been the headquarters of government ministers and Home Office, military and scientific personnel.
Now it is open to the public. Essex farmer Michael Parrish, on whose land it is built, bought it as a tourist attraction. Several thousand visitors have taken a guided tour of the twilight establishment, which, with the collapse of the Cold War, has been decommissioned.
He is keen to encourage schools to visit the bunker and get some idea of what went on during the Cold War. He believes that it is important for students of all ages to try to understand what would have happened.
He admits, "It is impossible for children to imagine the enormity of a nuclear attack, but taking them around the bunker, explaining what would have gone on and also giving them a film show, gives them a better idea."
Three storeys beneath farmland are a labyrinth of rooms capable of accommodating 600 people who would have been self-supporting for three months, carrying a brief to be a communications channel with surviving organisations and agencies above ground, and organising essential supplies and services.
The site for the bunker, at Kelvedon Hatch, Essex, was chosen originally for its closeness to London and to nearby North Weald air base.
It was built by the Air Ministry in 1953, and staffed by Fighter Command Metropolitan Sector radar operations centre. Later, in 1960, with the threat of a Russian nuclear attack, it became the Emergency Regional Government seat.
The land was owned at that time by Michael Parrish's grandfather. Under threat of compulsory purchase he was paid Pounds 2,500. Behind a screen of woodland a hillside was excavated to 125 feet (38m) and 10 foot (3m) reinforced walls were built. The bunker covers 21,000 square feet (1,950m2). On completion the earth was replaced to replicate a grassy hillside.
To complete the deception a bungalow was built, which doubled as the entrance to the bunker via a 100-yard (91m) tunnel, and the guard house. Armed guards were permanently on duty. They were replaced by unarmed Home Office personnel when the bunker "changed hands" and were stood down only in 1992 when the building was decommissioned.
Michael Parrish, who farms the land jointly with his father, recalls the strict security. "Although the guards knew me well whenever I came up to inspect the cattle in the nearby fields if I got too close they would call the police."
The whole operation was done in utmost secrecy. All building mat-erials were transported from a nearby railway station along different routes to avoid attention. Amazingly, the locals had no idea what was going on.
The bunker is completely self-contained with its own water supply and electricity generator. Staff could have remained inside for three months. Facilities included civilian and military operations rooms, a 24-hour canteen, a BBC studio where information and warnings could be transmitted to the population outside, a sick bay and operating theatre and rooms for use by scientists and government ministers, plus dormitories.
It was one of four key bunkers which could communicate with a further 2,000 much smaller ones networked around the country. All this was converted from its original use as a coastal defence centre and cost the government Pounds 10 million plus Pounds 3 million a year to maintain.
Although it stands on his land, Michael Parrish had to join many other eager buyers at public auction. His bid, which he refuses to divulge although the Home Office considered Pounds 100,000 a fair asking price, won the day. He has restored it himself with the help of enthusiasts like Reg Hills, who guarded the secret bunker for 28 years and used to patrol inside it every hour.
Open seven days a week, with tours plus film. Pounds 5 adults, Pounds 3 children. Special rates for parties. Underground Nuclear Command Centre, Kelvedon Hall Lane, Kelvedon Hatch, Brentwood, Essex, CM15 0LB. Tel: 01277