Hats off to the queen of New York

Nan Kempner, fashion doyenne and legendary socialite, has jetted in for Ascot - and for a little something to put on her head

" I 'm crazy about hats. I'm crazy about clothes. I'm crazy, period." Nan Kempner, social X-ray, international society doyenne, fashion queen and hat collector, is in her element, her famously bony arms reaching up to adjust the black feather ball of froth that Philip Treacy has just placed on her fabulously silvered hair. "This is my flirt hat," she says, admiring it in the gilt-framed mirror in Treacy's tiny salon. "I wonder if I'll have any success with it? It's probably 20 years too late for me. It's so terrific."

For most of her 60-odd years, Mrs Thomas Lenox Kempner, wife of the money- raking New York banker who works while she plays, has been famous for non-stop partying and shopping. She has missed only one of Yves Saint Laurent's couture shows since he opened his house in 1962, and stays thin as a wire coat-hanger by exercising fanatically. That way, she fits the samples which are sold to her at a discount. She is the thinnest, boniest, sharpest and one of the wealthiest of the shiny, glitzy international jet set.

Fashion designers from Valentino to Galliano love her almost as much as she loves them. Her circle of friends spans the world and she has met anyone who is anyone, from the Queen in 1997 to the Pope in 1951 (she wore a black mantilla). Her life is one long party. She danced with Halston, Valentino, in fact, anything that moved at Studio 54, and still has the most insatiable appetite for fashion, art, charity fund-raising and dancing, with a boundless energy that is infectious - even now, approaching her seventies. She asks Philip about the Bluebird, Terence Conran's new restaurant on the King's Road. "Can you dance there?" she asks, and immediately loses interest when she is told it is a dining room, not a night club.

Since arriving in London from New York, Nan has attended an intimate dinner for 10 with the Princess of Wales ("in a small group, she is so relaxed and full of charm," Nan confides), spent a weekend in the country with friends, and done just a little bit of shopping. At Erickson Beamon, the costume jewellers just up the road from Philip Treacy on Elizabeth Street in Victoria, she fell in love with a black and white beaded choker. "It makes me feel like Princess Je Ne Sais Quoi, it's almost like a face- lift," she laughs. And at Philip's she ordered a hat for Ascot and, as is inevitable for the woman who has spent her life-time shopping, took the feather cocktail number, too.

"I was obviously meant to have this hat," she says. She won't be wearing it to the wedding of Princess Zahra, the Aga Khan's daughter, tomorrow night, however, because that's far too grand an affair: a ball. To that, she will wear a gown by her dear friend, Oscar de la Renta. But no doubt over the next few weeks there will be the perfect opportunity for sipping champagne with the elegant little thing perched coquettishly on her head. "The time is right for glamour again. I was longing for something mysterious and glamorous, feminine and flirty, a crazy frivolous thing to pop on my head for cocktails. If I wear it to the theatre, I know I'll drive everyone crazy."

Not that Nan Kempner needs an excuse to wear a hat. She has worn them all her life. "The hat makes the occasion," she says. "It makes you feel flirty and feminine. Very sexy. A hat that takes you out of yourself; you go on a mental trip when you wear a sexy hat."

There is no stopping her, with or without headdress, although God knows, she has enough hats and feathers to go around half the population of Manhattan. She has kept them all, including the Adolfo man's panama, the veiled Dior cocktail hat, and the extravagant Philip Treacy feather halo she wore to the Fitzgibbons' wedding last June. Before Halston became the king of the New York fashion scene in the Seventies, he was a milliner for Bergdorf Goodman, and Nan was, of course, a devotee. In particular, she remembers the hat that made him famous: the pill-box that Jackie Kennedy wore. Nan had one too, but then she says, so did everyone.

Nan has decided that hats are back in fashion, and will almost certainly pick up a few more when she zips back to Paris in July for the haute couture shows, after a party in Provence.

"On a drear day," she says in her quick-fire American smoky rasp, "it gives me such pleasure to open the closet and look at my hats." The collection will have expanded by the time Nan arrives back in New York for the Princess Diana sale at Christie's, for whom she works as an international representative. She's busy gathering syndicates of friends to club together and buy pieces to donate to various museums around America. "I might buy one myself," she says.

"My love affair with hats started out in the baby carriage, with bonnets, ribbons and bows," she remembers. Then came the school hat to match a blue reefer coat, followed by her going-away hat, a Chanel straw boater, no less, to match her suit. Over the years, however, her trademark has become a Davy Crocket number from Yves Saint Laurent's rich peasant collection. "I wore that non-stop in cold weather, still do. It's become my trademark on the ski slopes." In warmer weather, when she's not on the slopes but basking on the sand of some tropical island, everybody knows it's Nan by the Philip Treacy straw with a helicopter blade on top. "Not only is a hat provocative, it's protective too," says the woman who has never held practicalities high on her list when buying clothes or accessories. She battles with skin cancers.

At Ascot next week, Mrs Kempner will make her entrance in a cream raw silk jacket and black skirt by her dear friend, Yves, topped off perfectly with Philip Treacy's deceptively simple, off-white wide-brimmed straw. "It's so nice to have a hat maker in my life again," she says. The two first met about six years ago and Nan has been enchanted by Philip's wit and whimsy ever since. "I've had such fun in his hats. He's a magician. Hats turn a girl into sugar and spice and all things nice." They also cover a multitude of sins. "When you put on a hat, it covers a bad hair day, a hangover, a saggy face. A crazy hat makes everyone who sees you smile." When Nan makes her entrance to the Royal Enclosure next week, there will be beaming faces everywheren