It is not, despite being tucked away behind the M25 in beautiful, secluded Essex woodland and being regularly visited by groups of OAPs, a nudist colony. During the Cold War years, Kelvedon Hatch was an intended regional seat of government, the post-holocaust hideout from which the great and the good would rule London and the eastern region.
Mr Parrish addresses the tour party in the style of a Crystal Maze presenter running a war-games exercise. "Imagine it's the sixth day of the war and the bomb has just gone off. You've been sent outside to run a little errand so you must now remove your clothes. Go through the decontamination unit and put them in a brick bin. Then shower and wash off the radioactive dust."
Holly, an anxious daytripper going underground for the first time, had been unsure what to wear. "I mean, what do you need for a nuclear bunker? We weren't sure about the footwear. Will we be walking through puddles? We've brought pullovers." Mr Parrish raises a bushy eyebrow and points to the overalls hanging up in the decontamination unit. "Okay? Right. You have enough food, water, air and power to last eight weeks. Let's go."
Holly says that she never realised the three-storey concrete tomb had been bang on her doorstep all those years. Our guide hopes this sense of amazement will bring in the locals, along with the usual coach parties of mast-spotters, military buffs and CND nostalgics. So he is playing the "Top Secret" card for all it is worth. Dotted along the narrow, winding country lane leading to the mysterious hole in the ground, tourist signs boast, "SECRET BUNKER AHEAD". A bit of a giveaway for Iraqi spies and the like. "If Saddam lets one off," smiles Mr Parrish, "we have got to be prepared to shoot people."
Armed guards were still defending the citadel, not so cunningly disguised as a farm cottage, as recently as 1994. Mr Parrish takes us through a 120-yard entrance corridor designed as a buffer against intruders. "It was not to keep the Russians out," he emphasises, "but to keep the likes of you and me out. The Government would be expecting riots and marauding gangs of people outside with radiation."
An air-raid siren wails in the background as he runs through the strangely familiar doomsday scenario. "Period of tension for two to three weeks. Conventional warfare then Big Bang. Flash would blind you, heat would burn you up and there'd be strong winds. Five days of lethal radiation. There'd be a military firing squad to maintain law and order outside, of course."
Such a macabre spin, apparently, greatly appeals to schoolkids doing GCSE history projects, who return home asking what their daddies did in the Cold War. Behind the giant tank-metal doors at the end of the tunnel lie a few clues: scrambler headphones, teleprinters, Protect and Survive leaflets and replica tins of condensed food. Mr Parrish has scoured the land for authentic artefacts and is on first-name terms with the country's major scrap-dealers.
It comes as something of a shock to discover a smiling John Major tucked up in a bunk bed. We have reached the second floor and are staring into a small room where a wax figure of the Prime Minister lies snugly under a blanket. Mr Parrish owns up to a bit of marketing licence, but insists a senior minister would have been stationed at Kelvedon Hatch; a regional commissioner given virtually unfettered powers to rule over the surviving population. "There might even be a danger he'd become a dictator." Michael Heseltine's name springs to mind.
If the Major puppet is straight out of Spitting Image, the main operations room is pure 1960s James Bond, and the makeshift morgue on the top floor a cast off from the Chamber of Horrors: loud groaning noises on the loudspeakers, bloodied "bodies" on the operating table and black bin-bags hanging from the walls. "Oooh look," laughs Holly, "cardboard coffins. I suppose they're easy to fold up."
Under threat of compulsory purchase, Mr Parrish's grandfather, a farmer and market gardener, sold the hilly wooded site to the Air Ministry in 1952. Immured a hundred feet beneath the ground, it was first used as a ROTOR early-warning system - part of an east coast chain - before being converted into a nuclear command centre.
Following the collapse of the Soviet Union, hundreds of bunkers were put up for sale. Some have been converted into document stores, film archives and even rave clubs. Others have become unlikely tourist attractions; 68,000 people visited Fife's museum last year.
Mr Parrish is keeping a watchful eye on developments in Russia and seems particularly interested in the resurgence of nationalism. "One scenario might be if the Communists got back in again and we had a Cold War situation and the odd two or three bombs were dropped. Not total war... more on the Chernobyl scale."
And what would he do if the panicky masses demanded entry into his secret fortress? "I'd keep them at bay, defend it in some way... using legal means of course."
Kelvedon Hatch Bunker. Open daily 10am-4pm. Info from Michael Parrish on 01277 364883
SOME VERY SECRET BUNKERS
Essex Secret Bunker, Mistley
Operational from 1951 to 1993, it has been fully restored and equipped by bunker expert James Fox (see bottom left). Sound effects fill the concrete tomb with "authentic noises" (air sirens) and a labyrinth of passages lead to the dormitory, radio room, communications centre and telephone exchange. The centrepiece is a giant two-level underground operations room. Visitors can reflect on the "secret world of nuclear government" in the Atoms Cafe, before being treated to a "spectacular show" in the main operations centre. Open daily from 10.30am-4.30pm to 29 Sept (01206 395680)
Cabinet War Rooms, Whitehall
Known more informally as Churchill's Bunker, this was the final citadel for Britain's Second World War leaders, covered by camouflage netting to keep the Luftwaffe at bay. In operational use from 27 August 1939 until the Japanese surrender in 1945. Highlights include the Central Map Room, where information on all fronts was displayed using coloured wool, pins and paper flags and a broadcasting studio from which, according to legend, David Niven would have impersonated Churchill in a final rallying cry to resist. Open 9.30am (10am from October) to 6pm daily (0171-930 6961)
Dover Castle's Secret Tunnels
Lying beneath one of England's oldest and largest fortresses, the network of tunnels housed the command centres which controlled naval operations in the Second World War, when the castle stood in the front line, directly facing German-occupied France across the narrow Straits of Dover. It was here, in May 1940, that the famous evacuation of British and French soldiers from the Dunkirk beaches was masterminded. Some tunnels date back to the 12th century, others were built 200 years ago in response to a potential French invasion. After the Napoleonic wars, they were used in the war against smuggling. More recently, they performed a nuclear command role before being closed by the Home Office in 1979. Open daily 10am-6pm, last tour leaves 5pm, to 30 Sept (01304 201628)
La Valette, St Peter Port, Guernsey
The Channel Islands were the only British territory to be occupied by the Germans during the Second World War - more than 12,000 troops were stationed in Guernsey. This well-lit, air-conditioned Nazi bunker contains a fascinating display of German military history and both occupation and liberation vehicles. Open from 10am-5pm (01481 722300)
German Military Underground Hospital, La Vassalerie, St Andrew's, Guernsey
First opened to the public in 1954, this is the largest construction on the Channel Islands, built by slaveworkers from France, Spain, Morocco and Russia - together with some Guernseymen - under the beady eye of the occupying forces. Almost invisible from the surface, this concrete maze of tunnels, covering 75,000 square feet, is built under a low hill in the heart of the Guernsey countryside. Between two main, parallel corridors are the wards, operating theatre and X-ray room. It took three-and-a-half years to build, but was only used for six weeks at the end of the war. Open 10am-4pm; 2-4pm in Oct, 2-3pm Suns & Thurs in Nov (01481 39100)
Scotland's Secret Bunker, Troywood, Fife
Lies 100ft below the sparsely populated east Fife countryside, fronted by a nearby farmhouse named, revealingly, "Whitehall". A nuclear command post from 1968 to 1993, "Scotland's best-kept secret" boasts an 1950s RAF radar room packed with screens that tracked Soviet incursions into British airspace, and a cinema showing hilarious civil defence information films; in the event of nuclear attack, cyclists are instructed to disembark and run for cover, while householders are advised to pack an overcoat. Open daily 10am-5pm (0333 310301)
The Bunker, Kirknewton, Midlothian, Scotland
The coolest rave club north of the border. Open from late-night through to the early hours of the morning. Most of the teenage clubbers passing through the iron doors don't realise it was a nuclear bunker as recently as 1992.
DDR, Cold War Bunker, Harnekop, Germany
Built under a military camp 40 miles east of Berlin as a bolthole for 500 Communist VIPs, it became redundant after the 1990 re-unification. Two-hour "very special interest tours" (in the words of the German Tourist Board) on weekends and holidays, taking in 180 rooms on three floors. (0891 600100)Reuse content