Step inside the shiny glass doors, however, sniff deeply on the perfumed air, so the legend goes, and you enter a different world. Sleek blondes in black heels are quietly concentrating on the serious business of high fashion shopping. Here is a navy jacket (pounds 480) and trousers (pounds 275) by Ter et Bantine; there a short cream coat (pounds 550) by Barbara Bui; and would Madam like to try the flame suit (pounds 1,025) by Calvin Klein?That white Kelly bag (pounds 325) by Alan Faye is tempting. But Madam is distracted by a vulgar woman in a scarlet jacket who has hijacked the sales assistant. "Lady Di bag," she barks. "Black. How much?" "Harrods," replies the assistant, directing her next door. Instead, our shopper's final purchase is a new body cream by Estee Lauder, price pounds 27. Then she disappears in a puff of perfume into a cab SW-bound, a little tired, several hundred pounds poorer, but what else is a Sloane to do on a Wednesday afternoon?
Such is the reputation of Harvey Nicks - the store's nickname for those in the know, including Ab Fab's Patsy and Edina on a shopping binge. While Harrods is a vast, increasingly tacky tourist mecca; Fortnum & Mason full of little old ladies; Selfridges too big and too bland, Harvey Nicks claims to be simply the most glamorous department store in London. Since its 1991 takeover by Hong Kong-based millionaire whizz-kid Dickson Poon (now 42) from the Burton Group, who had filled it with lots of rather dull carpets and lost money, it has been reinvented as the store of choice for the stylish rich and the seriously chic: Madonna is a customer; Princess Diana is reported to buy her bikinis here; only last week Emma Thompson - the epitome of understated English glamour - was there, searching for an Oscar gown, perhaps.
Otherwise, Harvey Nicks is favoured by the young and beautiful. In the darkly glossy bar - part of the Fifth Floor food and drink emporium - that stays open after the store has closed at night, I found Paula, a graphic designer in her late twenties, wearing leather trousers and a black polo-neck, drinking cappuccino with David, a photographer with long hair and a goatee, a couple of Dolce e Gabbana bikinis by her side. Downstairs, Deborah, 23, a freelance fashion stylist and student at St Martin's, had just spent pounds 79 on a little black bag. "If I could park," said Deborah, "I'd come here every week."
The formula has worked brilliantly: since 1991, turnover has gone up from pounds 54m to pounds 75m, profits from an operating loss of pounds 150,000 to pounds 6.5m in the black; coming this summer is a new restaurant on the top floor of the Oxo tower on London's South Bank; the autumn sees the opening of a store in Leeds. This week the company announced a stock market flotation to develop stores in New York, Paris, Tokyo and elsewhere in the UK.
But the true picture is more complex. Why, here in the Fifth Floor cafe are a couple of cosily overweight middle-aged ladies on a day out, in pastel knits, M&S skirts, gilt ear-rings and a nice matching scarf. Next to me in the bar - by 6.30pm, full of wideboys on mobile phones and singles on the make - are Maureen, 39, and Jeanette, 36. Maureen has bought a pair of tights; Jeanette says the cosmetics gifts are excellent. But the fashion? "I like Nicola [sic] Farhi," says Jeanette, uncertainly. "And is it DINKY [sic]?" Maureen is less equivocal. "A hideous mauve nylon shirt for pounds 99," she says, incredulously. "you've got to be kidding."
As for the illusion that Harrods is for herds of tourists while Harvey Nicks is for fashionable Londoners: these days the store is full of foreign money. Today, two heavily made-up Americans, possibly New Jersey Mafia molls, have taken over the Versace concession, clothes strewn across the little velvet couch. "Give me that in the green," snaps one. "Is that a jacket or a blazer?" says the other. "I'll take it anyway. In the green."
If the truth be told, Harvey Nicks is not just an exclusive club for the super rich, but a provider of escapist glamour for everywoman. "If you're depressed, there's nothing better than coming to Harvey Nicks," says Jeanette. Says Linda Grant, whose forthcoming novel, The Cast Iron Shore, is in part a history of shopping: "From time to time we need a bit of mindless glamour to cheer us up."
For most of us, this doesn't mean spending a fortune on clothes. Indeed, only 36 per cent of the store's sales come from women's wear. Thanks largely to the fabulous window displays (memorably a pink seascape constructed entirely from copies of the Financial Times), supercool ad campaigns (including the first homage to the Reservoir Dogs poster) and the glossy Fifth Floor food hall, where customers now spend 15 per cent of their cash, Harvey Nicks has become the chic place for a girls' day out. Once transported via a separate entrance and express lifts to the gastronomic delights at the top of the store, tradtitionally a dead shopping zone, they exit by escalator, passing by all the sartorial attractions at a leisurely browse. Such visitors may, once in a blue moon, consider buying something to wear but they are far more likely to visit the beauty salon (hair repair treatment, a mere pounds 10), or pick up a pair of DKNY tights (fashion accessories account for 12 per cent of sales). Back in the grimy hustle of Knightsbridge Tube station, they may feel a million dollars, but they've spent only pounds 15.
Harvey Nicks is a brilliant trick: in-the-know glamour for everyone, on a scale not seen since Biba in the Sixties. The illusion is contained in the details: the Fifth Floor cafe may have a modish, grilled vegetable- heavy menu, but also serves comforting great platefuls of chips, served with chic (but even more fattening) garlic mayonnaise - an affordable treat at pounds 2.75. The staff are presentable, but not frighteningly fashionable or too thin, as in the dauntingly cool cafes attached to Emporio Armani, or Nicole Farhi's Bond Street store. More importantly, service is quick enough to leave plenty of shopping time - even in a lunch hour.
All this democracy has its downside. (Indeed, a strange old man was buying bottled beer and endless tins of tomato puree when I visited the food hall.) "It's lost its soul," says one top fashion journalist. "These days it's like an airport lounge, predicated completely on the bottom line. For Dickson Poon, fashion is just another commodity. And the clothes are for sloanes who want to be comforted by names." The seriously fashionable now favour Liberty for its adventurousness and the support it offers young designers.
But as we've seen Harvey Nicks isn't really just for the seriously fashionable. It's an escapist day out for you and me, Maureen and Jeanette, and middle- aged matrons in M&S skirts: the new ladies who lunch.