The affluent residents of London's Cadogan Square were bewildered by the enormous hole that appeared in the back garden of their eccentric neighbour Hans Kristian Rausing shortly after two commercial airliners flew into the Twin Towers in New York.
While some panicked Britons stockpiled powdered milk and gas masks, the Swedish heir to the £5.4bn Tetra Pak carton empire had set about building himself a state-of-the-art nuclear bunker.
But there was no attack, nor, as we now know, were there any weapons of mass destruction deployable within 45 minutes. Mr Rausing – Hans K, to his friends – sold the property two years ago, luxury fallout shelter included, for £14m.
It is a sale he may have come to regret. After the turmoil of the past three months, he would have had few stronger urges than to take up residence in an airtight underground retreat with his family.
On Tuesday, at Westminster magistrates' court, the Crown Prosecution Service dropped charges against Hans K and his American wife, Eva, both 44, after large quantities of class-A drugs were discovered during a police raid in April at the couple's £5m Chelsea pile. Officers had found heroin and £2,000-worth of cocaine – enough to stun a baby elephant.
The whole shebang began when Mrs Rausing was allegedly caught trying to smuggle drugs into the American embassy, with several "wraps" of cocaine discovered in her handbag – an unorthodox approach to enlivening United States diplomats' customarily staid parties.
The incident came as a shock to the couple's families and their tight inner-circle of friends in London society, not to mention a huge embarrassment to the Prince of Wales, who is on first-name terms with the Rausings and once publicly described black-bearded Hans K as "one very special philanthropist".
It wasn't just the shocking revelation of the couple's use of "crack" – a cheap, smokeable form of cocaine, more commonly associated with Britain's sink estates than the chic dining rooms of Knightsbridge – but the manner of its discovery.
Such apparent stupidity – taking class-A drugs into what is the most heavily fortified London residence bar Downing Street – is explained, friends say, by the throng of addiction which has once again engulfed the everyday life of the Rausings. They still enjoy trips to the Royal Opera House, but are not the socially active couple they once were.
Their previous problems with substance abuse were well documented in society columns of the 1980s. They met at a rehabilitation centre in the US, where Eva had been sent to recuperate by her father, a wealthy executive of the drinks company Pepsi, and where Hans K was sweating out the excesses of his wayward youth.
He developed a drug habit after he famously upped sticks and left home at a young age to go and follow the hippy trail in India. His father, a 6ft 8in giant also called Hans who now sits at number seven on The Sunday Times rich list, moved the family from their homeland to London in 1982 to escape Sweden's punitive tax system.
Hans K showed little of his pater's entrepreneurial initiative, however. With cash available from trust funds and the famous Tetra Pak fortune, Hans K decided to drift. As one family acquaintance says: "Where else was he to go? He had no discernable interests anyone knew of, and his dad had made more than God. It's not as if he was going to make any more."
The couple gradually became regulars on the London party circuit and could be found at the polo on Smith's Lawn in Windsor Great Park. But Hans K is not considered a natural conversationalist. "They would be out quite a lot and then before you know it they'd drop completely off the radar and not resurface for months," says an acquaintance from the 1990s. "You never really knew what to make of them."
The couple built a £15m home in Barbados not far from the Sandy Lane Hotel, the fashionable retreat part-owned by the horse-racing magnates JP McManus and Dermot Desmond.
Mrs Rausing's family had also built a home there and so it was widely thought that the decision to move in such close proximity to her own family was a sign that she had finally laid her demons to rest. But the addictions have returned repeatedly. The couple became generous supporters of the Mentor Foundation, the drugs prevention charity active in 40 countries, which was founded by Queen Sylvia of Sweden in 2000.
Company accounts show that in the past few years alone, Mrs Rausing, who is usually hidden by sunglasses, has given Mentor's Shoreditch office more than £600,000 in seven years.
That generosity aside, the magistrates' leniency towards their latest brush with drugs was greeted by widespread disgust, chronicled in certain sections of the press. The judgment, so generous that the pair won't even receive a criminal record, appeared to confirm that old adage of "one law for the rich and another for the poor".
Here was a couple with every opportunity and privilege their respective families' wealth could afford – and whose legal costs alone would probably dwarf a top public school's yearly fees – escaping with nothing more than a gentle slap on their (Rolex-braceletted) wrists.
The frustration of the Metropolitan Police Commissioner, Sir Ian Blair, was palpable. Two years ago, he vowed to crack down on drug use among celebrities and the middle and upper-classes – a pledge that has since invited ridicule with both Kate Moss and Amy Winehouse escaping penance despite the incontrovertible photographic evidence of their drug abuse appearing in the red-tops.
Sir Ian commented this week on the Rausings' reprieve: "I do find that result extremely surprising. And it reminds me of the 19th-century legal comment often attributed to Sir James Mathew: 'In England justice is open to all – just like the Ritz.'"
For all Hans K's generous philanthropy – The Royal Opera House has also benefited from his largesse – he was a particularly easy target for the press as he didn't appear to do anything. In the past, he has loosely described himself as a "financier", a job title – like its housewife equivalent, "the interior designer" – which has been employed by many with a six-figure sum nesting in their current account.
This apparent lack of graft contrasts in sharp relief with other members of his family. The aforementioned Hans Snr, 81, who keeps a stuffed wolf in his East Sussex conservatory and breeds wild boar and deer, continues to make canny investments with his self-acquired fortune. His two daughters enjoy using wealth to pursue their interests.
The youngest, 45-year-old Sigrid, who lives with the award-winning film producer Eric Abraham in Holland Park in one of London's most elegant private residences, which has its own two-acre garden, owns the high-brow magazine, Granta, which she rescued from near extinction. She also set up the edgy publishing label Portobello Books, albeit backed by the Tetra Pak squillions. Similarly, the eldest daughter, Lisbet, 47, attended Berkeley and Harvard and holds a PhD in anthropology.
Hans K's first cousin Kirsten is known in the horse-racing world as a successful breeder. She owns Lanwades Stud in Newmarket, where, by all accounts, she has never been afraid to get her hands dirty.
But the family remain a closed shop to the press. It's not just a mistrust, common among the rich and famous of the cynical nature of the media, but also the fear of the dangers which exposure to the public at large can bring: namely, kidnapping.
Like many whose wealth is often tallied in the various rich lists that appear in publications each year, the prospect of abduction preys heavily on the mind.
The story of John Paul Getty III, who was nabbed in 1973 and whose severed ear was delivered to his father along with a ransom note, remains a terrifying wake-up call to members of the world's exclusive billionaire class.
Unlike Mr Getty, though, who has never fully recovered from his own addictions brought on by the traumatic ordeal, the Rausings, that most peculiar of couples, now has a chance to get their lives in order.
The magistrates' leniency stemmed in part from the Rausings' commitment to seek professional help to save them once again from the spiralling vortex of addiction. That is a place from which no one, not even those with customised nuclear bunkers, can expect to hide.Reuse content