Imagine it's Saturday night and you're in your local casualty - you've hurt your finger, and you are facing a long, painful wait surrounded by vomiters, drunks and bleeding children. If you knew you could nip down the road, be whisked through a pleasant (deserted) waiting area, into the arms of a calm, fully-trained doctor or nurse - at a price - would you do it? For most people, the answer to this is yes, depending on the cost. Those made of sterner principles (or with no money) might say "never". But what if it was your four-year-old daughter with the wound?

This is what the founders of Emergency Plus, Britain's first 24-hour, seven day a week walk-in private casualty unit, are banking on. The unit is located in a converted supermarket in the leafy Surrey village of Byfleet, just inside the M25. I confess that I visited it with my hackles up, fully prepared to object violently to the whole enterprise as part of a private trend that will further bleed the NHS of staff and divide our society into first and third class citizens. I had visions of a bunch of money-grabbing charlatans, who get you through the door with your painful wound, whisk your credit card from your shaking hand, then stitch you up and bill you massively for hidden extra costs.

The brainchild of Angie Liston, a local business woman (with private individual backers), Emergency Plus is, however, far less threatening than I'd imagined. It was conceived out of Liston's despair at having to wait in casualty with her small son and his scalded foot. In purely business terms, it's a bold endeavour, given that the competitor is a monopoly, a household name and offers the same service for free. But the notion of private emergency care is not new - it works in countries like the States, Australia and South Africa where all medicine is private. And Emergency Plus has a pretty vulnerable "target client base". If you're bleeding to death on the forecourt, you're not going to care how much it costs you to go inside. And even if you don't think you're going to die, with a basic "consultation fee" of £25 most people with an income would be prepared to cough up simply not to have to wait for six hours in a busy A&E.

I was given a tour by practice manager Dr Johan DuPlessis, a South African, who reassured me that they simply want to provide us with "choice". The waiting area is all carpets, pot plants, copies of Country Life and free coffee. There's even a health food shop if you're peckish. Not that you'll spend much time waiting. "I can," says DuPlessis, "go from one to five doctors in an hour". Apparently the unit could cope with up to 200 "clients" per day, though so far the most they've had is about 30. There are five doctors on the staff - none of them fumbling, sleep deprived trainees - who work eight-hour shifts, as well as nine nurses. And in case of mass accidents (presumably) there is a bank of 3,000 doctors to call on. They can't guarantee you won't have to wait, but they're certainly having a good go.

The facility isn't actually a fully-fledged A&E - although they have all the gurneys, swabs and defibrillators to cope, initially at least, with trauma. The "clients" they want to attract are those who don't need hospital back-up (like major surgery or intensive care). My vision of the smiling receptionist turning away car crash victims was punctured by DuPlessis, who reassured me that the Hippocratic Oath still counts in Byfleet. In a dire emergency his staff would stabilise the patients before transferring them to the local hospital.

But to style yourself as a "24 hour doctor and emergency service" is, according to Mr C A Perez-Avila, consultant in accident and emergency medicine at the Royal Sussex hospital, "taking quite a risk". Though he believes that "anything that removes minor injury patients from a busy A&E is good", Perez-Avila sees a minefield of potential disasters when you start advertising yourself as an emergency service: "What might seem a minor case of tummy ache could quickly turn out to be a ruptured ectopic pregnancy," he says, "in which case you need - rapidly - the blood transfusion facilities and other resources that only a hospital can provide." The time you take to get yourself to the walk-in clinic, rather than dialling 999 for an ambulance to casualty, may mean the difference between living and dying.

So although such a clinic may seem to offer patient choice, for those needing "the full spectrum of a major acci dent and emergency department" this choice may be a perilous one.

Emergency Plus's preferred target group is those not in dire need of emergency care, who can afford to "take their health into their own hands". So you can skip into the clinic on a whim at 3am and have a vasectomy (£195 for the op, plus £200 for an on-call surgeon). Indeed, 24 hours a day you can get your cholesterol level tested, have a mole removed, have a "well-woman" (or man) check up, get inoculated or have your leg sewn up. In affluent Surrey, packed with business people not known for their social conscience who need out-of-hours facilities and can afford to pay for them, this surely is an astute business idea.

But the introduction of payment brings with it other grey areas. What would happen, I inquired, if I had a heart attack now on the doorstep, was revived and transferred to the local hospital? Would Emergency Plus charge me even though I didn't choose to come here? The answer is a qualified yes. Assuming I survived, I'd get a nice letter with a bill for the equipment used, plus the transfer to hospital (£515.93 - it happened to a man last week). And what if I couldn't pay? Then I'd be treated like any other "bad debtor". Of course, the board of directors would use their discretion (I assume they wouldn't charge my bereaved family if I didn't make it.) Well, this is business after all.

The local community seems to have few qualms about the new clinic. "I think it's a good thing," says a nearby pharmacist. "I'd pay to use it rather than wait in casualty." Local GPs apparently refer people to the clinic, the clinic refers people to the local dentist and even those who couldn't afford to use it themselves, don't see it as an outrage. "You can still go to St Peter's [in nearby Chertsey] or Guildford," says one elderly woman. For most people it comes down to affordability. And prices don't seem exorbitant. Break your leg - in a straightforward way - and you'll get a bill for around £85; your finger needs six stitches, that'll be £45. An asthma attack will set you back about £68. You're advised of costs every step of the way. But then, who, faced with a nice doctor poised with an anaesthetic is going to say: "Forty five pounds! That's ludicrous! I'll take myself off to the A&E for a five hour wait."

Choice is, then, a muddy concept when it involves pain and fear. Still, many of my concerns were put to rest by the unit's adherence to official NHS policies. What, for instance, happens if a "client" brings in a child with a suspicious injury? If they are paying for treatment, does this change the relationship with the healthcare provider? I was assured that Emergency Plus would follow NHS procedure here, just as they would if a mentally ill person asked for treatment for self-harming injuries. But if this is the future of emergency medicine, and such outfits proliferate, others may not be so trustworthy. There is plenty of room for abuse - unnecessary procedures, for instance, poor quality care or simple over-pricing.

This particular unit is regulated by West Surrey Health Authority, which has "free access" to all the clinic's records, though quality of care is self-regulated. It seems unlikely that over-stretched health authorities would have the resources to inspect and regulate a national proliferation of Emergency Pluses. And they do intend to proliferate. There are plans for another two units in close proximity to Byfleet, and ultimately a nationwide network. Since no insurance company will cover emergency medical care, such enterprises are destined forever to be the privilege of those with money. But if they are really just dealing with minor injuries, while offering a range of fancy facilities (like complementary medicine and dietary advice), they differ little from existing walk-in clinics, many of which are struggling to find "clients". Having said that, if I sliced my finger open, I might still hold out in casualty, but if it were my child, I'm sure I'd be down at my local Emergency Plus before you could say "hypocrite".