ARCHITECTURE: Wibbly, wobbly and wonderful

Jelly Babies, according to the cheery slogan on the packets, "live in a wibbly wobbly world of their own".

Stepping into Ron Arad's north London studio, the same unsteady property appears to apply. This is one of the oddest offices in London, a timber, steel and PVC ellipse holding in check topsy-turvy floors, curly-wurly walls, complex chairs packed in boxes that mimic the shape of their content while doubling up as chairs themselves, and a small, cosmopolitan team of architects.

The day I wibble and wobble up the uncertain iron stair to Arad's Chalk Farm think-tank, it is raining cats and dogs and water is gushing into buckets in the middle of his workshop, courtesy of clumsy builders at work next door. As the studio resembles the sort of fish tank Captain Nemo might have dreamt up to decorate the Nautilus, (with a little help from the mature Barbara Hepworth), the sight and sound of splashing water seems a comfort rather than a distraction. And, anyway, you expect the unexpected here.

Mr Arad's studio might be a thing of strange shapes and forms fantastic, but it is also the source of truly inventive art, furniture and architecture that has, over the past 15 years, invaded the conscience of collectors, art galleries, restaurateurs, international furniture manufacturers and, in Israel, the world of opera.

Perhaps more than any other architect at work in Britain, Mr Arad links the awkwardly "elliding" worlds of fine art, craft, industrial design, interior design and architecture. For him, there is no obvious gap between art and architecture. The foyers he completed last autumn in the new Tel Aviv Opera and Performing Arts Centre are like an art installation, while his art installations have animated some of the world's most architecturally challenging new galleries, including the Fondation Cartier, Paris, designed by Jean Nouvel.

As well as bridging the art gap, Arad knows, while being serious and thoughtful, how to make his work entertaining and even funny - which is why the bizarre, seemingly faddish, yet hugely successful Belgo diner, in Chalk Farm, London, hired him to double its size. By happy coincidence, the restaurant is next door to the architect's studio. He is now designing a new 400-seat Belgo in Covent Garden.

At Belgo, the very latest in interior design and furniture meets a popular and appreciative audience. This is one of those rare and special moments when the avant-garde is instantly digested and the architect, performing at the cutting edge of his profession, pirouettes effortlessly down from Parnassus to the marketplace, this one alive with mussels and awash with beer.

Next Tuesday, at the Royal Institute of British Architects, Mr Arad will explain to a packed audience (he always draws a crowd) in his enigmatic way - at once self-deprecating and bullish - how he applies much the same apparently uncompromising approach to the design of shops, restaurants, offices, opera houses and, of course, furniture.

Arad (who was born in 1951) is still best known for his furniture, beginning with the highly successful Rover chair of 1981 which became a studied design statement in the reception areas of upbeat advertising agencies and recording studios at the height of yuppiedom. He made the furniture himself with a small team of aesthete-welders. As the Eighties rushed towards their fall, the designs became increasingly big, increasingly outlandish and beautifully resolved. Things for sitting on had become not just funky, but fine art and big money (although not, of course, for the designer).

In the leaner Nineties, Arad is designing cheaper chairs for industrial production, while continuing to experiment with one-off designs as a form of research and development and a way of making ends meet.

"Architecture is rarely very profitable," he says. "What I would like to do is to make a chair for production as simple, as sculptural and as popular as Arne Jacobsen's famous plywood Ant chair. Perhaps you know that more than 5 million of these little chairs have been made, from Denmark, a little country. That's at least as many Ant chairs as Danes [5.1 million] - not bad, eh?"

Not bad. Like Jacobsen, whom he greatly admires ("we have Ant chairs at home - I can't make anything better myself"), Arad comes from a small, industrious country, Israel (pop: 4.9m). He was born, brought up and educated in Tel Aviv, studying at the Bezalel Academy of Art before coming to London in 1973 and picking up his studies at the Architectural Association. He set up his furniture-making business, One Off, in Covent Garden in 1981, establishing his own architectural practice, Ron Arad Associates eight years later.

Today, he has furniture mass-produced outside Milan ("workshops on the edge of Milan are a delight," says Arad, "they don't understand the meaning of `can't be done, guv' "), is a professor of architecture in Vienna and does all his design work in London ("the most creative capital city, if not a place to get things done").

An internationalist, his architectural team is cosmopolitan, the bulk coming from Canada, drawn from there by his professional partner Alison Brooks. Together they make the unlikely and the sculptural real: bronze walls, for example, in the foyer of the Tel Aviv opera house, begin as a screen that wraps around a column, folds into a bench and then becomes a wall again making an enclosure for the opera's bookshop.

Elsewhere in the opera house, a free-standing island pavilion provides a swooping sculptural space for an amphitheatre, 200-seat cafe, kitchen and bars at four levels. The sci-fi walls are shaped from sheets of steel and concrete and broken apart at one point by what looks like a free-standing stair veneered in bronze. Imagine being able to climb up into, say, a Hepworth sculpture, and to eat and drink there: an odd notion, but one that Arad and Brooks make possible.

If you cannot afford the trip to Tel Aviv, you can enjoy something of the same sculptural magic in Chalk Farm, or later in the year, in Covent Garden (Belgo, not the Royal Opera House). Arad's genius is in making the avant-garde accessible, affordable and entertaining. He is becoming a populist without having to compromise his art and has become a professional without buttoning up and doing the right thing.

Although he made his name in the Eighties with expensive hand-crafted furniture for highly paid high achievers, the Nineties will be much more his decade, when a younger generation of British patrons will ask him to design free-style buildings and he will prove that he can rival the great Arne Jacobsen by designing a mass-produced chair to rival the plywood Ant, at a price many of us will be able to afford.

When that happens, Mr Arad's once exclusive world will be one we can all share, if not quite as readily as a packet of Jelly Babies.

Ron Arad talks at the Royal Institute of British Architects, 66 Portland Place, London W1 on 21 February (non-members £5.50); 071-580 5533.