The Priory, the favourite clinic of celebrity addicts such as Kerry Katona, has just been bought by an international consortium. But what's the key to its phenomenal success? Terry Kirby reports
It has been a place of refuge at moments of crisis for everyone from Kerry Katona and Shane MacGowan to Kate Moss, and at any one time you could probably cast at least a couple of celebrity reality television series from its list of patients.
While others prefer vomiting therapy among the Buddhist monks in the Himalayas, having their blood changed in anonymous Swiss establishments or the charms of a detox at the Betty Ford Clinic in California, the Priory Hospital in south-west London has become the destination of choice for many celebrities when grappling with the bottle, multiple drug abuse or just plain old-fashioned 'stress' after too long on the showbiz party circuit.
Now the value of those celebrity customers "who bring the ordinary punters close behind them" has been made abundantly clear with the sale of the company which owns the Roehampton establishment for £875 million (?1,289 million) to ABN Amro.
The key to this massive valuation is partly based on the fact that for several years now, the Priory has seemed an almost inevitable destination for many, once all the right buttons of celebrity have been pressed.
Take Kerry Katona. This is a young woman possessed of suitably enhanced and photogenic looks, formerly an Atomic Kitten, winner of a celebrity reality series, married and then separated from a former Westlife member Brian McFadden. She has also endured a particularly torrid time at the hands of some sections of the media, and, lo and behold, suddenly finds herself at Roehampton and 'in rehab', being treated for an addiction to anti-depressants.
It's about as predictable as seeing her on the pages of Heat magazine, falling out of the Met Bar or Chinawhite.
Julian Linley, the magazine's deputy editor, believes celebrities like Katona pick the Priory largely because it's an easy option.
"It's a bit like eating at the Ivy," he says. "There are lots of other great restaurants to go to, but people choose it because it's simply the familiar and easy place to go. They know the Priory because its got a name you can remember and it's close to central London, so all your friends and family can come to visit you.
"And if people are having problems, it's where their friends tell them to go, because it's the first place to come to mind."
Indeed, the list of former patients is long - Kate Moss went there for treatment after splitting from Johnny Depp, while her current boyfriend Pete Doherty has received treatment for his heroin addiction. Comedians Lenny Henry, Caroline Aherne and John Thompson have had treatment.
Others who have been helped there include the footballer Paul Merson and several members of the rock aristocracy, including Eric Clapton (cocaine) and Ronnie Wood (alcohol). The 'It' girl, Lady Isabella Hervey, was treated for bulimia, the television presenter Gail Porter and the stepdaughter of actor Pierce Brosnan all checked in.
For a basic rate of around £650 (?958) a day, celebrities get access to some of the best specialists in treating addictions and stress problems in a plush, hotel-like environment, where many of their whims - apart from those relating to the finest wines or lines, of course - are catered for.
While the media like to stress the luxurious nature of the Priory, the reality is not quite the same. "I think a lot of celebrities like it because it actually feels more like a hospital than a health farm. There is a sense that they are getting genuine treatment. And sometimes in the company of National Health Service patients," said Mr Linley.
A former senior doctor at Roehampton says: "It's definitely not a health farm, and I would say that the ambience is more three-star than five-star. I think the place is a bit second-rate, frankly: some of the carpets are worn and the paint is peeling.
"And the staff there are like Harley Street."
Another issue, he said, was the recidivism rate of patients."I think most people would actually get as good a deal going to one of the Betty Ford or other clinics in the United States - like Naomi Campbell has - rather than be under the spotlight at the Priory," he says. "But people tend to go to the Priory as a result of word-of-mouth recommendations for the most popular doctors and consultants."
Although most celebrity patients at Roehampton fund themselves, the majority being treated there and at the group's other hospitals have some kind of private health insurance, usually related to their profession.
Recently the group has launched advertising campaigns in newspapers to target high-flying City workers with alcohol problems - most of whom have some kind of private health insurance. Britain's Ministry of Defence last year signed a three-year £5 million (?7.4 million) contract with the group to treat service personnel.
Celebrities and City executives are the most high-profile element of the Priory's business, but the group makes the bulk of its money in other ways.
It has expanded the bread-and-butter side of its operations, and likes to stress its work with young people suffering from conditions such as autism and Asperger's Syndrome, along with its clinics dealing with neurological rehabilitation.
The bulk of these patients - as well as a small number at Roehampton - are referrals from Britain's National Health Service. It is believed that around half the group's total business comes from patients passed from the state sector.
William Lang, of the healthcare analysts Lang and Buisson, says: "Although it attracts attention, the celebrity side of the business is only a small part of the group.
"There are quite a few areas where they are the only serious presence, and they receive a substantial number of NHS referrals because there is no state provision - such as the special schools for treating children with disorders, and the clinics dealing with rehabilitation for people suffering from brain injuries."
This week's sale of the group will swell the bank balance of the Priory group's chief executive, Dr Chai Patel, who owned around 14 per cent of the group.
Dr Patel bought the Priory group in 2000 from an American concern which had owned it for more than 20 years. Since then, it has added 11 sites.
The group now includes 15 psychiatric hospitals, seven schools, two therapeutic community assessment services and five brain injury and rehabilitation units. Many of its hospitals are housed in fine listed buildings.
Although the Priory Hospital has only recently come into public notice thanks to the public's obsession with celebrity, it is, in fact, London's oldest private psychiatric hospital.
It has been in continuous operation since 1872, when Dr William Wood, one of the first modern psychiatrists, moved his patients from Kensington to Roehampton to benefit from the calm atmosphere and clean air of the countryside.
On its website the group states that its overall vision is "To bring hope, healing and sanctuary to all the patients, pupils and residents who need our services."
And that's even if the worst thing to happen to them is having taken part in a celebrity reality show.