Five miles outside the town of Chippenham in the rolling Wiltshire countryside a precious treasure is stored in a very unlikely location. Buried deep under 100ft of clay and encased in millions of tons of limestone, nearly £1bn worth of fine wines sits safe from prying eyes and unwanted attention.
As my taxi pulls up outside the main gate at Corsham Cellars security is obviously tight. There are motion detectors, razor wire, huge steel doors and 24-hour guards that James Bond would struggle to overcome. All of this technology is designed to protect acre upon acre of Châteaux Lafites, Pétrus, Latours and Margauxs, which have literally been buried underground in a disused mine.
"The locals call it the wine mine," my friendly country cabbie tells me as I get out to confirm my identity at the security desk. "My daughter used to work down there for a while; it's a funny place, like a set from The Avengers or something."
Global demand for fines wines has soared in the last five years and while the Bordeaux bubble, where wealthy Chinese investors bought the 2010 vintage at almost any price, burst in June of last year, demand is still solid. A case of 1982 Châteaux Lafite, for example, will still set you back nearly £30,000, explaining the thorough bag search and security questions from the site's burly guards.
And there is no sign the trade, and the need to store fine wine safely, is likely to fade away. "There has been a slight dip in prices but in the long term they will remain high because there are more and more customers from Europe, Russia and the Far East competing for what is a limited amount of fine wine, says Richard Harvey, international director of wine at the auction house Bonhams.
With such large sums of money at stake, storing fine wine in an old rack in the corner of a draughty kitchen or in the garden shed is no longer an option. So much so that there are now seven million bottles stored underground at Corsham Cellars. Run by Cert Octavian, a company that specialises in looking after the finer things in life, the mine was previously owned by the Ministry of Defence. It spent millions of pounds making it suitable to store explosives and ammunition during the Second World War but since 1989, when the labyrinthine underground site, which spreads over one million square feet, was bought by the businessman Nigel Jagger, its corridors have been stacked with wine, not TNT.
"To store wine correctly humidity, temperature, air quality, light and vibration must be tightly controlled to ensure it matures at its natural rate and doesn't deteriorate," Jagger, chairman of the company, says.
"Our customers are very knowledgeable now and know that wine stored in direct sunlight or in a room that is too hot or too cold can be damaged. An average temperature between 10C and 15C is ideal.
"In hindsight, the attributes underground at Corsham are perfect as we are insulated by natural rock and have a constant temperature. All we need to do is tweak the humidity and ensure a smooth flow of fresh air passes through the mine."
Working underground can be dangerous, and before we climb down the 157 steps to the wine vaults, Ella Lister, a wine-industry consultant who works for Cert Octavian, fits me out with an emergency oxygen supply and high-visibility jacket. It costs customers £15 per year per case to store their wine in the vault and the average price of a case ranges from £1,500 to £3,000, rising to as much as £100,000, she says as we descend. As well as the major auction houses and wine suppliers, the company's customers include Andrew Lloyd Webber, the venture capitalist Guy Hands, chef Michel Roux Snr, a "very famous" Premiership manager and several Hollywood stars whose names a tight-lipped Lister won't divulge.
Underground the air is dry and the atmosphere eerie. Several scenes from The Guns of Navarone with Gregory Peck were filmed in the mine and Second World War graffiti – not all of it polite – stills adorns the walls. Just down the road is Burlington, Britain's now-defunct nuclear bunker and the place to which the Prime Minister and the Royal Family would have fled if the Cold War turned hot. It's not hard to imagine the piles of bombs and ammunition that would have been stored here.
Now there is only wine. And lots of it – about 700,000 cases in total. Each has a barcode and its exact location is stored in the company's computer, while a staff of 100 underground workers work in three shifts to keep things in order.
"Provenance as well as security is important to our customers," Lister says, as we pass a particularly valuable case of wine owned by a wealthy investor she dare not name. "For example, if a customer wanted his or her Lafite 1989 brought to the surface to drink or to sell, we'd never just bring the nearest case of that vintage up. We'd make sure it was that customer's exact case. And with so many bottles, our records have to be top-notch."
According to research by the company, keeping fine wine in a quality cellar like Corsham can add as much as 20 per cent to its value come auction day. But as Jagger explained before he left us at the surface – his bad back means he prefers not to tackle the stairs too often – it's the Second World War-era levels of engineering that make the site viable.
"Thanks to a box ticked by a pen-pushing Civil Servant back in 1936, the MoD spent millions on high-quality galvanised ducting that runs through the mine. It's still solid after all these years and means we can bring a totally new supply of fresh air down every half an hour for perfect storage conditions," he says.
What the soldiers working down here during the Second World War would have made of all this decadent wine in their former armoury I'm not sure, but they'd probably have thought much the same thing as me: "where can I find a corkscrew?"
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