It's the jolly green giant of US food retailers, selling 'natural' produce on a scale barely imaginable on this side of the Atlantic. The name Whole Foods Market mightn't currently mean a lot to Irish shoppers, but the company which has transformed the way Americans buy their fresh food is hungrily eyeing the Irish market.

The company will open its first British megastore in London next month, and indications are that Dublin is also on its list. If that proves the case, Irish shoppers should prepare to be astounded and overwhelmed.

Whole Foods is totally unlike any food retail chain ever seen here, either in size or philosophy. It sells every kind of fresh food imaginable, trading on a determinedly green, environmentally friendly image. Its buzz-words include organic, ethical, sustainability and humane.

The company, now the world's largest natural foods retailer, was founded in 1978 by John Mackey, a 25-year-old hippie philosophy graduate and his 21-year-old girlfriend Rene Lawson. They borrowed $45,000 from family and friends to open a small, resolutely vegetarian food store called Safer Way in Austin, Texas.

Its clientele were mainly students and alternative lifestylers. The produce was supplied by local farmers. The name over the door was a kind of student joke - a play on the name of the giant Safeway chain. When the couple got booted out of their apartment for storing food products there, they simply moved into the shop.

From these unconventional beginnings rose an entirely new kind of retail colossus. A series of aggressive takeovers of other natural food chains means that it now has over 300 stores in the US, Canada and Britain. Last year its turnover was $5.6 billion.

What emphatically sets Whole Foods apart from all other retailers is its dogged adherence to its founding principles, and the physical enormity of some of its stores. Its new outlet in Kensington will be on three floors, covering an incredible 80,000 square feet. That's around the same size as the city's new Wembley Stadium.

To most of us, eco-friendly means small - niche producers supplying a limited market. But that's not the way Whole Foods sees it. The company has taken consumer interest in naturally produced food on to a whole new commercial and presentational level.

Its attractive store lay-outs feature every conceivable fresh food product - fruit, vegetables, meat, fish. There are cheeses, deli goods, beers, wines, a bakery, mini restaurants and even organic cosmetics. No taste is too sophisticated to be catered for. If an item isn't available locally, it can be flown in.

Feng shui consultants help the store design; no two ever look the same. The stacks of mouth-watering displays are enhanced by ambient lighting and mellow music. The entire effect has been termed 'food theatre'. Every effort is made to make the Whole Foods shopping experience as pleasant as possible.

The company's philosophy includes some sparkling examples of New Age guff: "We believe in a virtuous circle entwining the food chain, human beings and Mother Earth; each is reliant upon the others through a beautiful and delicate symbiosis."

US shoppers clearly love the concept. The company's expansion has propelled it into the Fortune 500 list. It is now so big that it is frequently mentioned in the same breath as the (still much bigger) Wal-Mart. Some observers, dismayed by its rapid growth, have even dubbed it Whole-Mart.

John Mackey, now 54, has been described as the Bill Gates of organic foods, but he wilfully refuses to live up to the standard tycoon image. Despite being one of the shrewdest operators of his generation, he comes across more as a parody corporate hippie who disregards normal business convention.

A vegan, he spends as much time as possible on his 720-acre ranch near Austin where he and his wife Deborah practice meditation and yoga and raise their own free-range chickens. He doesn't draw a salary and has donated his stock options to the company's charities.

"I have enough money," he declared last year. "My deeper motivation is to try and do good in the world."

But Whole Foods succeeded because Mackey didn't let his personal beliefs cloud his business sense. He told one interviewer: "When we opened a bigger store, we made a decision to sell products that I didn't think were healthy for people - meat, seafood, beer, wine, coffee. We were a whole food store, not a holy food store."

A striking example of how Whole Foods differ from other outlets is an insistence that all their meat is produced with the least possible cruelty. They consulted with animal welfare groups before drawing up humane treatment standards for farm animals and birds. It's idealism, but not as we generally know it.

'I think one of the most misunderstood things about business in America is that people are either doing things for altruistic reasons or they are greedy and selfish, just after profit," says Mackey.

"The whole idea is to do both. The animals have to flourish, but in such a way that it'll be cheap enough for the customers to buy it. We don't think there's a contrast between sustainable or ethical issues and bottom-line issues."

For ten years running, Fortune magazine has placed Whole Foods among the top 100 US companies to work for. But Mackey's hippie rhetoric is occasionally sprinkled with shards of glass. He is vehemently anti-trade union and once infamously compared unions to a dose of herpes.

Whole Foods have been in the UK since 2004 when they acquired the Fresh & Wild natural foods chain. The Kensington store will be the first under the company's own banner. Many more are planned.

According to regional vice-president David Lannon, "We're looking at 30 to 40 stores in the UK high street at the rate of one a year."

An outlet here would undoubtedly be welcomed by Irish food lovers. But it would be bad news for most other fresh food retailers, especially those serving smaller niche markets. The US experience has been that smaller shops are driven out of business by the new neighbourhood giant.

And truly green shoppers will be faced with another dilemma. Whole Foods says it does its best to source produce locally, but it has no qualms about also bringing produce, if necessary, from the far side of the world. Are you really helping the environment by purchasing an organically grown vegetable that has had to be flown several thousand miles?

In truth, only about half of the Whole Foods produce range is organic. Critics in the US - particularly New York Times journalist Michael Pollan - have raised major questions about the company's green credentials. Its Achilles Heel is undoubtedly the vast food miles that are routinely clocked up to fill the beautifully lit shelves.

But make no mistake - if Mackey decides to open here, Irish food retailing will never be the same again.