In 1992, residents of the rural Essex village of Kelvedon Hatch, England made a shocking discovery. With the Cold War at an end, the government decommissioned nuclear bunkers across the country and locals were startled to find that what they had believed for decades to be an underground reservoir was in fact a top-secret subterranean shelter.

Today, the 35,000 square-foot (3,251sqm) space still sprawls 80 feet (24m) beneath farmland belonging to Mike Parrish, a fifth-generation farmer and the grandson of Jim, who sold the land to the government back in the 1950s.

Click or scroll on to tour this intriguing government facility...

In 1952, Mike's grandfather Jim was approached by the British government. They wanted to buy a 25-acre (10ha) field at the centre of his 2,000-acre (809ha) farm just outside this small, sleepy village of Kelvedon Hatch. Jim was threatened with a compulsory purchase order if he didn't agree to sell the field, but luckily he was happy to.

"My grandfather said he had fought two World Wars and wasn’t inclined to fight another," Mike says. Despite negotiating a price for the land, Jim wasn't able to wangle a spot in the bunker for his family should the worse happen.

Today, the Parrish family owns the land once again and Mike runs tours of the secret nuclear bunker.

The Air Ministry bulldozed the existing hill and posted RAF guards to stop anyone snooping on the building works. Above ground, all that can be seen is a car park and this rather non-descript bungalow, which is actually the guardhouse. Designed to resemble a typical 1950s farm cottage, its deceptively innocuous appearance conceals steel shutters, bombproof doors and a false roof masking an 18-inch (45cm) reinforced concrete ceiling.

"The walls are twice as thick as you would expect of an innocent farm cottage," Mike says. "It was built, not to keep the Russians out, but the likes of you and me."

"I was a young child then," Mike recalls. "I remember seeing the blue RAF coaches coming from North Weald every shift, because it was originally manned by RAF personnel. We have an S-bend on the main road. The coaches used to race and one of them turned over, which was a bit of local amusement. So yes, we knew it was here."

Mike and his family even watched the bunker being built, albeit covertly; signalling to each other when the guard turned his back and it was safe to look. Construction started in October 1952 and it was made fully operational in May 1953, just seven months later.

Thankfully, we're able to see inside this extraordinary site today because Mike, pictured here in 2000, bought back the land. In 1994, Prime Minister John Major began to sell decommissioned bunkers and the Parrish family snapped up Kelvedon Hatch via a sealed bid at public auction. They didn't want someone else operating the bunker, which sits right in the middle of their farmland.

Mike had imagined the bunker would be a dark, dank, cave-like place, but when he first entered it he was surprised to find it was light and airy, with "gleaming polished floors, mahogany banisters and lino glistening like ice."

The entrance tunnel is 120 yards (109m) long. It looks much like a corridor you'd find in any large facility – except for these bags holding old fashioned geiger counters hanging on the wall. 

The Bunker itself had three lives during the time it was operational. First, for about fifteen years, as a ROTOR Station, providing an early warning system. It then had a very short period of time under the Civil Defence. Then in the late 60s it was converted into a Regional Government Headquarters, which it was right up to the end of 1992. As the London headquarters, it would have sheltered the Prime Minister of the day, along with their cabinet, in a nuclear emergency.

The long entrance tunnel would be easy to defend against an intruder. It's protected by two sets of blast doors, which are made from tank metal. Had the first set of blast doors given way during an explosion, the blast would have come down the tunnel, hit the wall at the end, changed direction and lost a bit of its power and pressure before hitting the second set of doors. 

When the doors are shut, 600 or so inhabitants could have lived underground for up to three months, or as long as their food and water lasted. The facility has its own electricity and water, as well as air-conditioning, heating, humidifying, de-humidifying and chilling – it even has its own sewage fields out in the woods.

Once you’re through the blast doors and into the tunnel, you're 80 feet (24m) below the surface. If you look up this stairwell you can see that the bunker is on three levels. 

Once construction on the bunker was complete, the Air Ministry builders buried it once again. It's surrounded by gravel, to act as a shock absorber, so if a bomb did go off locally the bunker would shake, rather than collapse. They also buried concrete rafts in the surface to strengthen the top, along with 24,000 gallons (109,000L) of water stored in tanks on top of the bunker's roof. 

"I don’t think that in 1952 we fully appreciated just how desperate the government thought it was," Mike says.

Builders poured concrete 24 hours a day into the walls to stop it layering and causing weaknesses. Because it was wintertime, they burned wood in braziers all around the outside of the site to keep the frost from damaging the concrete.

"I must say, I still find it a little amusing that in the height of technology, when we were building H-bombs, they were still scrabbling around outside looking for wood to keep the frost off," Mike considers.

Once inside the bunker, it feels – as one visiting school group put it – like an upside down Norman castle

The Home Office left this Short Term Plan hanging on the wall. It shows a plan of the shelter and how it would have accommodated 600 people in an emergency. 

"We do have dormitories but to accommodate the extra people they thought they might need, they’d have put 48 three tier bunks down the right-hand side of the tunnel and then lockers would have been all the way down the left," Mike explains.

Further inside, is the Home Office radio room. In the village of Kelvedon Hatch, there is an enormous mast with dishes on it and a red light at the top. This is the Q-Met Mast – 'Q' indicating its secret status. It is part of the UK's National Strategic Communication Network and there's one mast approximately every 25 miles (40km) along the backbone of the country. They’re built to withstand an atomic blast and the bunker is connected to the Kelvedon Hatch mast by deep underground landlines and by a microwave dish. 

The communications rooms, the military and the plant and machinery which runs the bunker are all on the bottom level of the shelter, which was deemed to be the safest. 

The telecoms room contained over two and a half thousand telephone lines coming into the bunker. Latterly, more modern fibre-optics, which are more resistant to the electromagnetic pulse, were added along with a digital telephone exchange.

"When they decommissioned this Bunker back in 1992, they unfortunately gave that nice digital computerised type telephone exchange to the Metropolitan Police," Mike explains. "What we have now is the generation beforehand, the Strowger system, which is much more interesting because at least it sounds and looks like a telephone exchange."

Alien to us these days, the teleprinter was the main form of communication at the time. Cables were buried deep underground where they were thought in theory to be immune from the blast.

They were operated using a punch tape. This is not code, as lots of people would like to imagine. It simply enabled telexes to be sent more quickly and more cheaply this way. The message only needed to be typed once onto the tape and could then be sent to many destinations.

When the bunker began life in the 50s, it would have used the same plotting system as had been used in the Second World War. Around 15 to 20 WAAF officers would have plotted planes on a giant map, while controllers would use that information to deploy aircraft.

Radar changed everything and the plotting table was made obsolete. Between this bunker and one in Bawbaugh, Norfolk the skies of England and most of Europe were watched 24 hours a day.

"We did the daytime and Bawbaugh did the night-time," Mike explains. "Except for Wednesday afternoons, when we played football. I’m not quite sure what happened then!"

The walls of the bunker are made from 10 feet thick (3m) concrete, reinforced every six inches (15cm) by one inch (2.5cm) thick tungsten enhanced steel rods. Round that they put a brick and pitch waterproof membrane and a mesh Faraday Cage.

When an atomic bomb goes off it creates an electromagnetic pulse, which wipes out all things electric – cars, phones, radios, computers and also the National Grid. The Faraday Cage around the bunker would have protected the sensitive electronic and communications equipment inside.

Also on this floor were the scientists. It was their job to determine where the bomb had gone off, how big it was and how high above the ground it had burst. They would then authorise various warnings.

A black warning meant that the fallout was imminent and a grey warning meant it was due within the hour. A white warning gave the all-clear. We would already have had the red 'attack' warning. Known as the ‘Four Minute Warning’, it would have been broadcast from the main BBC Bunker at Evesham. Upon hearing it, civilians were to climb under their kitchen tables, which they would have covered with bedroom doors and mattresses, and hope for the best.

The arrival of fallout would have been heralded by three loud bangs, or if you lived in Scotland, the tolling of church bells. The all-clear, just like the Second World War, was the straight note on the siren. However, ideally, the public could be instructed over their ordinary domestic radios – hence the bunker's fully soundproofed BBC radio studio.

In the period of tension, before the bomb was expected to go off, the government would instruct everyone to switch off and disconnect their radios, push in the aerial, wrap the radio in tinfoil or put it in a biscuit tin to make a mini-Faraday cage, and not switch it back on until after the bomb had gone off. In theory, they would then still work – although there was no guarantee. 

From this very room, the Prime Minister – most likely Margaret Thatcher, who was in power from 1979 to 1990 – would have broadcast to the nation in the event of an emergency. The bunker's powerful transmitter was capable of transmitting to the whole of the world.

Mike was fortunate that a number of photographs existed showing what the bunker looked like while it was active. The family was able to acquire some of these and they also employed a guard who had worked on the site for over 29 years, so they had first-hand information when reconstructing the bunker.

There are eight different ways of sending communications in and out of the bunker, but the main way to send and receive warnings was via the red war phones. These were connected to a system called ‘Carrier Control’, which was linked to about 1,400 police stations, fire stations, council offices and individuals in remote villages who would rush off outside and let off the sirens. 

This room was known as the secretariat, where the typists would have been stationed. Mike and his family held a reunion lunch for some of the people who had worked in the bunker during its first life as a ROTOR station, and they shared their thoughts and memories of their time there.

They revealed that the bunker had to scramble British aircraft at least once a week. It was often the Russians testing to see how quickly the British could react or trying to get in and out of the radar undetected, which in the early 1950s was still quite primitive. However, Friday night was the busiest night of the week, thanks to American airmen flying planes without permission from Europe to London in search of a good time. 

In fact, Mike and his family have had a number of bunker parties over the years. Within a week of buying the bunker they threw a party.

"I think we had about 200 people down here. And the memorable thing about that was we were all enjoying ourselves when suddenly we were invaded by an awful lot of burly policemen. The Home Office had forgotten to disconnect the alarm and one of our guests set it off." It being the 90s, they thought an illegal rave was taking place.

"We've had lots of fun parties down here," Mike recalls. "But it's not necessarily the venue that makes it fun, it's the people you're with." 

Mike can be seen here showing off the bunker's impressive air conditioning compressors and air scrubber. The facility is powered by two Dale generators. They’re propelled by two Rolls-Royce diesel engines and there is enough fuel buried in the ground outside to last at least three months.

The Bunker is also connected almost directly to the National Grid from two directions. Everything has at least one backup and sometimes more. 

This instrument would have detected any nuclear explosions and estimated the size in megatons. It was known as A.W.D.R.E.Y., which stands for Atomic Weapons Detection Recognition and Estimation of Yield.

If a nuclear blast had occurred in the UK, only around three or four million people would have survived and prospects would be grim, according to Mike. Temperatures would drop to between -20ºC (-4ºF) and -40ºC (-40ºF) and there would have been no harvest for at least three years. The first would have been burnt off by the flash or the cold weather. Survivors would be too lethargic and radiation levels too high for the second. For the third, you’d have to scrape away the contaminated soil and sow by hand any seeds that you hadn’t already eaten.

As well as Geiger counters, anyone who left the bunker after a nuclear attack would worn a Dosimeter on their lapel. Inside the tube, a dial would tell them how many Roentgens of radioactivity it, and therefore you, had absorbed.

75 Roentgens was the acceptable wartime level. Once you got to 150, you started to feel a bit sick. 

The harsh reality is that, within a very few days of an atom blast, the bunker would have run out of essential drugs such as morphine. This room was used to store back-up batteries, but it also doubled as an operating theatre.

With six hundred people down here for three months and the nearest surviving hospital maybe hundreds of miles away, illness and injury was likely. For those who didn't make it, there was a supply of coffins made from cardboard, because they folded up to save space.

There are only 200 beds in the bunker, including ones erected in the entrance tunnel, so people living in the bunker would have used the 'hot bed system'. One bed would be slept in by three people, each one claiming the bed for an eight-hour sleep over 24 hours.

While the living quarters of the Prime Minsiter or the bunker commissioner may have been a little better, Mike nevertheless likens the bunker to a "concrete coffin".

"For me, if a nuclear attack happened I would certainly come down into my bunker," Mike told British newspaper The Metro. "My wife wouldn’t, interestingly. A lot of people say 'I’d rather stand outside and be evaporated'. I think it is important that people take on that challenge [of trying to survive]. Human life is important, someone’s got to be here at the end of the day."

In an emergency, the kitchens would operate around the clock to feed each shift as it came on and off duty. Food would have been brought into the bunker as the atomic threat grew and stored in every space available – under beds, in cupboards and under tables.

The bunker didn't have freezers, washing machines, dishwashers or lifts – electricity and water would have been at a premium and so all the food would have been dried, tinned or pre-packed like these rations found in the bottom of each bedside locker.

While Mike won't reveal how much he paid for the bunker, we do know it cost £1.5 million (roughly £36m/$46m today) to build in 1952. In the late 1960s, another £10 million (£140m/$178m today) was spent converting it into a Regional Government Headquarters. £19 million (£37m/$47m today) was earmarked to modernise the equipment here and add another floor on the top of the bunker by the mid-1990s, but this never happened.

During its active lifetime, the facility cost around £3 million a year to run on standby – that would have been around £54 million ($69m) at the height of the Cold War in 1962. Mike believes it would cost more than £100 million ($127m) to build an equivalent bunker today.

Despite the bunker needing ongoing renovation, it was active when the Parrish family bought it, so they found it in good state. Despite this, Mike's advice to anyone wanting to buy a former government bunker is to have deep pockets.

Thankfully, the bunker is a popular tourist attraction and Mike vows to keep it open for as long as the public keep coming. He even hires it out as a filming location. Other uses that have been considered over the years include data centre, valuables storage, religious retreat or electronic testing.

Despite welcoming a number of paranormal groups over the years, Mike hasn't encountered any ghosts himself and insists the bunker doesn't have any sinister undertones.

However, he does get the occasional enquiry from people looking for a safe space during times of global instability. For example, more than 200 people contacted him after the 9/11 terrorist attack, and there has been renewed interest since Russia's illegal invasion of Ukraine.

This secret exit tunnel could have been used by people slipping in and out of the base to covertly gather supplies in a post-nuclear world. In contrast to life in the bunker, the world above ground would be a scary place. Marauding gangs of people with radiation sickness would be a constant threat. 

"They’re not being fed, they have a limited life span and what they want is your food," Mike says. "There’s not much of a sanction against somebody with a limited life span. In effect, in all respects, you’d be going back to medieval times."

The bunker has provided much-needed additional income when times have been tough for the farm and it has given birth to other attractions, such as aerial wires in the woods and the UK's most award-winning mud run obstacle course. Above all, Mike says that owning this unique piece of history has given him a sense of pride. However, it has also opened his eyes to the reality of nuclear war.

"I think Einstein summed it up very well," says Mike. "He said that if the next war was fought with the atom bomb, then the one after that would be fought with bows and arrows."

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