The model agencies say one of these girls is the proper shape and the other is too fat. Are they right?

A concave chest, pin-thin arms, and jutting hip bones can propel a teenager to catwalk stardom - or straight into hospital with a feeding tube down her nose. Model agencies are once again in the dock amid claims that an eating disorder is an advantage for young girls hungry for the fame and fortune that life as a clothes horse can bring.

The line that divides teenagers with a physique envied by millions of women from that of the anorexic is increasingly blurred, despite agencies' protests that they employ only healthy girls with normal appetites who are thin because they exercise a lot.

Jo Fonseca, director of Models 1, said: "Models have to be slim. I can think of nothing worse than being fat. The only reason that thin girls look so unusual at the moment is because there are so many fat people."

Anecdotal evidence suggests otherwise. Lynda Thompson, 18-years-old, 5ft 9in and weighing in at just 61/2 stone, was in the first throes of anorexia when she was stopped by a scout for a leading agency and asked if she wanted to be a model.

"She said I had a perfect figure and walked beautifully, so I was just right for the catwalk," Ms Thompson said. "For the past year my family and friends had been telling me I looked awful and needed medical help ... It was so confusing. I thought 'I can't be too thin if an agent thinks I'm good enough to be a model'. So I continued to starve myself." Six months later she was dangerously ill in hospital.

Amy Davies, who worked for a top agency, allowed herself just 400 calories a day in order to maintain her 34-24-35 figure. "Sticking to the statistics on my modelling card was becoming a real struggle. I'd go to casting or shoots and ... people would say to me 'you're a big one aren't you'," she said.

In a third case detailed in the October issue of Company magazine, 17- year-old Lucy Stanley, 5ft 8in and under 91/2 stone, was told by an agency to come back only after she had lost two stone. Ironically, two years ago Lucy had been two stone lighter; she was fighting anorexia and bulimia. "My cheeks were hollow, my eyes had sunk into my face and my skin was terrible, but then the agencies would have wanted me," she said.

A leading fashion photographer told the magazine that "superwaifs" often faint because they are starving. "One model I was working with collapsed in a heap during a shoot. We tried to get her to eat something but all she'd have was rice cakes."

The leading agencies all deny knowingly hiring anorexics, or encouraging slimming to dangerously low weights. But Kelly Penford of Boss Models admits that if an agency looks after 300 girls, some do have eating disorders. "But we work very closely with dieticians and nutritionists and we get worried about girls if they lose too much weight," she said.

Dr Dee Dawson, an eating disorder specialist and founder of the Rhodes Farm clinic in north London, is adamant that many models are anorexic because it makes them more successful. "What these model agencies is doing is irresponsible. They don't care about the damage they're doing to these girls."