Icing on the cake or pie in the sky?: Harvey 'Shop-till-you-drop' Nichols has a surprise in store, finding room at the top for an elegant restaurant and food hall. Jonathan Glancey reports

HARVEY NICHOLS vies with Liberty for the status as London's most distinctive department store. What sets it apart is that it is the large shop for people who hate large shops.

A cornerstone of Knightsbridge shopping, 'Harvey Nicks' has always been a deb's delight. Perennially chic, it sells clothes and furnishings on an exclusive basis - you come here to buy glamorous things that you cannot find in other stores; and to be part of London's serious shop-till-you-drop scene. It has changed hands just three times in its 180-year history, each successive owner being keen to maintain the store's reputation for selling classy, distinctive goods to classy, distinctive people.

Over the past year, however, Harvey Nicks has begun to change - dramatically. Its latest owner, Dickson Poon, a successful 36-year-old entrepreneur from Hong Kong, has been pumping millions of pounds into the store since he bought it last year for pounds 57m. His ambition is not just to keep the distinctive tag, but to make Harvey Nichols one of the best shops in the world.

Now he hopes to attract established and new customers to spend even more time and money here with the opening of the store's roof-level food hall, bar, cafe and restaurant next month.

Traditionally, Londoners do not regard a department store as a place for glamorous eating, day or night. The best stores serve grown-up nursery food in timeless settings; lunch and tea are the meals that count. Yet here are Mr Poon and his catering director, Dominic Ford - formerly of the Mandarin Hotel, Peking - investing a lot of money (they will not say how much) on a vast food emporium.

When the store closes in the early evening, the food hall - inspired by the success of the Dean & DeLuca delicatessen in Manhattan, the grazing ground for upwardly mobile foodies - will act as deli, traiteur and grocer until 8pm, and the Fifth Floor, a restaurant, cafe and bar will stay open until 11.30pm.

Whether the Poon and Ford gamble pays off depends on at least three things: the quality of the food (both to eat and to take away), the design of the revamped top floor and, oddly, whether people can cope with a food complex five storeys above the London traffic.

This last point might seem slightly absurd; yet there is a notion among food retailers and restaurateurs that customers will be tempted in only if they can see, and, even better, smell, what is on offer inside. Anyone who walks past the Algerian Coffee Shop in Soho, or Kensington Place restaurant in Kensington Church Street, knows they have a point. Ironically, the Fifth Floor is based to a large extent on the astonishing success of Kensington Place, which has been full since it opened in 1988. The attraction of Kensington Place has not just been the food and the location but also its elegant design, by the architects Wickham Associates. Messrs Ford and Poon had no hesitation in commissioning Wickhams to design the Fifth Floor. For the food, they turned to another cool, fashionable modern eaterie, albeit a vastly more expensive one - Bibendum - and hired Henry Harris, one of its chefs. Julyan Wickham has designed the kitchen to Harris's personal specification - a sign of the confidence of Poon and Ford in the chef's abilities.

Now that Mr Poon's culinary venture is nearing completion (it opens on 16 November) it is possible to take a gamble and say that, if the Fifth Floor fails to come up trumps, it will not be for lack of taste: both Wickham and Harris have that in plenty.

Poon's and Ford's job is to encourage people to scale the baroque heights of Harvey Nicks day and night and to overcome the idea that eating in (or, in this case, on top of) a department store is some sort of social and gastronomic gaffe.

They can rest assured that Wickham has come up with the goods: the design is excellent. He has a long history of designing bars and restaurants, starting with the Zanzibar Club in Covent Garden, with fellow architect Tchaik Chassay, 15 years ago. This spawned a whole new generation of inspired architect-designed bars, restaurants and clubs in London including the Groucho Club, 192 (both by Tchaik Chassay), the Zen chain (designed by Rick Mather), and three restaurants in the City for the wine merchants Corney & Barrow as well as Kensington Place. The last four were all Wickham designs.

What the architect has done at Harvey Nichols is to seize the opportunities offered to him by a top-floor location and push them gently to the limits. At the core is the food department, where you can buy much the same food that Harris cooks; the idea is that unlike rival department-store food halls that sell brands that customers can find elsewhere (if not always cheaper), Harvey Nichols food will be special - selected by Harris's and Ford's buyers and chosen to reflect the chef's cooking. There is, to date, nowhere like this in London.

It is lit from above by a glazed zig-zag steel-and-glass roof, rather like those found in old market halls. This overcomes the traditional problem department stores have of relatively low ceilings on their upper floors; Wickham has opened up the ceiling to let the London sky in.

Flanking the food hall - clean, crisp and modern and made of expensive and durable materials - are the cafe, bar and restaurant. The restaurant is defined by a subtle, barrel-vaulted ceiling, which again belies the fact that diners are on top of a department store.

Wickham's decor will be as subtle - not-quite-white paintwork, white linen tablecloths, sparkling light, tightly-jointed wooden floor - as Harris's menu promises to be.

The chairs, designed by the architect, will not be like those of Kensington Place, Dominic Ford promises. He means they will be comfortable. The cafe, under the same serrated roof as the food hall, is a tall, bright and airy place, its big, east-facing windows looking over the baroque penthouses, domes and weathervanes of the parent building. Day or night, this should be an enjoyable place to meet, not least because here is a venue that anyone can come to and sip a cappuccino or toy with a tiny salad without fear of being ejected.

The bar, like that of the Zanzibar, follows a zig-zag path; the idea of this is not to represent a sense of inebriation, but to allow a larger number of people to sit at it.

What will make the Fifth Floor substantially different from the other modern restaurants, cafes and bars in central London are its location and likely clientele. A heel's click away from Harrods, Harvey Nichols nests in a bed of international wealth. Here are some of London's glitziest hotels - the Sheraton Park Tower in the shape of a giant dustbin right next door, and the Hilton across the southern slopes of Hyde Park. Surrounding it, too, are the kind of mansion blocks favoured by resident Americans, Japanese and Koreans who like to eat in those places rarely frequented by Londoners and common tourists because of the prices charged and the soulless, ersatz glamour.

'We hope the Fifth Floor will be a real mix of people,' says Ford, the man who must make it work. 'We don't want it to be a jet-set hangout but a real part of London.'

The Fifth Floor at Harvey Nichols has all the right ingredients; it would be sad if so much talent ends up - as certain rivals must be hoping - as pie in the sky.

(Photographs omitted)