There is a point where the road suddenly turns into a mock-country lane, then a gravel track, lined with meadowsweet. And tucked oh so discreetly away is the sign, the Priory Clinic. Beyond that there are cars - Mercedes, Jaguars, BMWs, Audis, Volvos and 4x4s; plenty of parking. As a visitor, you are directed to a lovely Georgian front door, kept invitingly open, with pillars, original curving handrail and steps.
This is the plush outer suburban world of the private mental health chain, a world away from the louche Kate Moss celebrity image of the group's flagship Priory Hospital in Roehampton, London. It is the solid tail of what is in reality an eye-wateringly expensive chain of 40 or so clinics and centres, rarely glimpsed, serving the despairing Home Counties gin-jag-substance-abuse classes, the prosperous deep south-east.
This Priory presents itself with arriviste comfort rather than borrowed glamour. When I first started making visits to a relative, I was so taken in by the name and the image that I kept looking over my shoulder, wondering whom I might encounter hover- ing between treatments.
On first contact it looks exactly like a country-house hotel. Beyond the door, in a perfectly preserved Georgian room, there are smiling receptionists flanked by expensive flowers, and a coffee table with newspapers. The furniture is good - well, reproduction; the gardens are lovely - and secure. When you ring to inquire after a person's health, the phone is answered within three rings, in line with best customer practice. You are put through to rooms where patients have privacy and en suite shower rooms (no baths). There are no restricted visiting hours, and it took several weeks to work out that the series of patients' rooms off a long corridor actually operated like a conventional ward. Windows open only so far; there is nowhere to jump, no sharp edges, not a chance of harming yourself. When someone at risk is on 24-hour suicide watch, the nurse sits in a wing armchair by the door.
And the conventions of English life are observed: tea and biscuits in the afternoon, placed in the residents' lounge; coffee in the conservatory. This is alongside lots of medication, however.
Signing the black leather entry book, you can't help but imagine the self-made multimillionaire visiting his depressed wife and thinking: "I'm giving her the best money can buy." You are safe inside, safe from yourself. Though it is not so easy to catch a doctor who can tell you anything.
The Priory message is that addictions, depression, mental illness are nothing to be ashamed of. You can be helped by firm, loving care - but at a price. At the beginning of this month the Priory Group was sold by its founder to the investment group ABN Amro for £875m, a price that amazed many in the City. Yet there is a burgeoning customer base of mental, self-abuse and addiction sufferers whose condition may not be extreme enough to warrant "sectioning" and restraint in an NHS mental hospital, but whose suffering is deeply distressing for families, companies and organisations. The Priory makes its money, for example, when someone fails at suicide, is treated by an NHS hospital and discharged home, distressed. The fees are £550 a day.
The group gets 70 per cent of its income from public sources, although that is not only from the National Health Service and includes specialist services for children.
There may not be celebrities to ogle, but there are definite Priory types. One set is the tall, distinguished, often rather head-turningly good-looking men who might at first sight pass for actors. But no, they are officers from the armed forces, recovering from the rigours of military life. I surmise most of them are drying out, because although they say hello they are guarded. The Ministry of Defence has a contract with the Priory organisation (for three years, at £5m per year).
Next, there are some rather thickset men with tattoos, in tank tops, a few also sporting heavy gold jewellery. They are harder to place: a mix of other ranks, self-made businessmen. They spend a lot of time communing with the sports pages.
Third, there are nervy City traders and brokers: youngish, thin men, by and large, addicted to their mobile phones and gadgets. One says he told his wife he was reading goodnight stories to their child when in reality he was wolfing down cocaine and pills after work. Another confesses to concealing hard drugs in a golf hole on a home putting green. Yet another says that the molehills on his Home Counties mini-estate made natural hidey-holes for his substances.
Then there are the desperate housewives: depressed, suicidal. On hot afternoons this month they sat on the grass getting tanned, sharing Cadbury's Fruit & Nut bars. One, recovering from a second overdose, praised her 15-year-old daughter for holding the fort at home.
Some of the men have bandages around their wrists and don't speak. The women tend not to injure themselves, and chatter a lot about gardens. Quite a few are blonde. There are anorexics, who hide away, and there is someone who is so very obese that a charity has sent her 200 miles to submit to six months' treatment and a restricted diet. She is cheery, and lies on her bed painting. The Priory has special tilting beds for such chunky patients, to keep them breathing.
One of the most shocking things is that everyone smokes, and chain-smokes outside. One woman tells me that, from five cigarettes a day, she is up to more than 20 now because, for all the treatments and routines, the yoga, anger management, self-esteem and cognitive therapy classes, there is nothing to do, bar watch television and go for escorted walks with nurses, if you are well enough. Being kept safe is boring. Everyone has plenty of money for fags. No alcohol is allowed. On my last visit, some women were holding a cheese-and-water party.
The other distraction is to eat the food: simple, lovely English cooking, served by waitresses and cooked to order, of the sort Loyd Grossman aspires to for the NHS. I imagine Gordon Ramsay drooling over the bread-and-butter pudding.
If you're paying £550 a day for the stay and the total charge for treatment is the cost of a terraced house in Liverpool, I guess that is only to be expected. One woman says that, because of the bill for treatment, she and her family will be lucky even to go camping this year.
At weekends, the garden and corridors echo with children - little children, hyped up, pleased to see their mothers or their fathers. Two, aged eight and five, were playing with water pistols at the weekend as the family dog bounced around with a visiting dad. The suicidal mother confessed that her two-year-old was too much of a handful.