SOPHIE DAHL has long legs, wild hair and a famous family. It should surprise nobody, therefore, that she is being tipped as the newest pretender to the supermodel crown. But she has one attribute that her similarly lanky, tousled and well-connected ch ums Honor Fraser and Iris Palmer lack: a figure. Sophie is an unabashed size 14 and sports a 38DD bosom.

It is a revolutionary departure for an industry that regards xylophone ribs as sexy that she has not been laughed out of the door. Still more surprising is the fact that Storm, the agency that signed her up, has made no demands that she go on a lettuce -leaf and water diet. What is going on?

There are two explanations. The first is that since the watch company Omega threatened to withdraw its advertising from Vogue in protest at the gauntness of the models, a sense of realism has weakened the superwaif's bony grip on our perception of beauty. The second is that telling Sophie to diet doesn't work. The last time a modelling agency was unwise enough to try, she went home in a rage and consoled herself with chocolate cake.

Sophie strides into the Storm offices off the King's Road, a 6ft Juno on 3in heels, biting the heads off defenceless jelly babies. In her grandfather Roald's book, The BFG, she was immortalised as the Big Friendly Giant's sweet little bespectacled sidekick, but these days she's more of a BFG herself.

"I still can't believe I'm here," she says, murdering another Jellytot. "I really thought I was destined for a life chained to a typewriter. I'm not knocking being a secretary, but it isn't a career you can get excited about, is it?"

Her preference for partying over homework, she explains, led to her leaving college two months into her A-level course. This academic laxity, however, was to lead indirectly to her new career.

"Mummy and I were having a huge argument on a street corner about my prospects. I was screaming, 'I'm not a failure, I will have a proper job, you'll see!' " Fortunately, the row took place outside the house of Isabella Blow, fashion's eccentric doyenne and a noted talent spotter. "I was sitting on a doorstep crying, when a taxi drew up and a hat got out," says Sophie. "I saw these little legs and a tiny bottom in lace trousers, and I thought, 'God, she looks cool'."

The feeling was mutual. Half an hour later, Blow informed Sophie's mother, the writer Tessa Dahl, that her daughter had a new career. "Issy thought Ellen von Unwerth [the photographer] would love me, so she took me along with her to shoot a Spice Girls album cover, pretending I was one of her stylists. About halfway through the shoot, Ellen came up to me and said, 'Hmm, who are you? I like you!' and took two rolls of pictures."

Others, however, were less susceptible to Sophie's charms. When she turned up with Von Unwerth on a prestigious assignment for Italian Vogue, the stylist was horrified.

"She was such a bitch," says Sophie. "All the other girls were really thin, but they happily accepted my size. But the stylist was furious. She said, in front of everyone, that I was enormous and she couldn't do anything with me. I felt so humiliated, I went and cried in the loo." In the end, Sophie was photographed wearing a carving knife, an ostrich feather fan and a furious expression.

"I was furious," she says. "It was the stylist's fault; she'd been sent my measurements weeks before. It was her job to get clothes to fit me, not mine to fit her clothes."

That was months ago. Now, Sophie finds that posing alongside size eight models holds no fears. "Actually, I love it, because I can eat lunch and they can't." She won't exercise, goes out for greasy-spoon breakfasts (though she doesn't order fried bread any more) and can't say no to rice pudding.

She doesn't know how much she weighs; in fact, she hasn't stepped on to a pair of scales since she almost succumbed to an eating disorder when she was 14.

"My mother and I had been living in an ashram in America," she says, casually, "and I longed to be a swami when I grew up. Then it all turned nasty and we had to run away in the middle of the night. I'd loved the ashram, and I was furious with her for taking me away. So I stopped eating as a way of gaining control over some part of my life."

In the end, the boredom of calorie counting proved her salvation, and she began eating normally again. "Dieting is a horrible way to live," she says. "I feel so sorry for some of these models who have to diet to stay all bones and hips. It's not humanly possible that they're naturally that shape, and I don't think it's at all sexy. In fact, it's sick."

Sophie believes the fashion world is ready for a change. "We've had the waif for the past five years; it's time for a different look." But it is premature to trumpet the return of realism to that looking-glass world. Although models are supposed to be selling clothes to normal women, they are still required to be built as much like coat-hangers as possible. Real women were never meant to wear clothes, it would seem: a bosom stops a dress hanging properly, while hips spoil the line. This explains why, despite the rapturous reception photographers have accorded the voluptuous Sophie, they all seem to prefer her with her clothes off.

Her first assignment, with Nick Knight for the fashion bible Visionaire, left her clad in just her contact lenses. "Mum thought I was going to be posing for a porn mag," she says. "During her modelling days, she'd experienced too many photographers s aying the picture wouldn't work if she didn't wet her T-shirt. She told me not to do it, and then all the family started calling. I said, 'I'm 19 - and if it's a mistake, it's a mistake, but it's important for me'.

"The shoot was absolutely terrifying. I was standing naked in the changing room, with the stylist powdering my bottom and covering my legs with foundation. It was surreal. But I really loved the pictures in the end. I looked like a Fifties pin-up. I didn't recognise myself."

She went on to be photographed for Vanity Fair in big knickers and stiletto heels. How fine is the line separating such photographs from those in a men's magazine? She looks appalled. "There is a Page Three mentality in this country," she says, "and having a shape is equated with sex. But I'd never do glamour shots - I couldn't."

Sophie believes Roald Dahl would have been proud of her career: "He always wanted me to do what made me happy." Her ambition, however, is to follow in his footsteps. "I'd like to buy a little villa in Italy and write all day, with lots of sweet babies running around and a divine husband," she says, dreamily. "But that means I've just got to make a lot of money modelling."