In nearly two decades at the helm of Britain’s leading fashion magazine, Alexandra Shulman has tended to side with the industry in the argument over the size of catwalk models.

In the past she has argued that “not many people have actually said to me that they’ve looked at my magazine and decided to become anorexic”. She still maintains that the use of thinner models is “not a health issue” but is simply out of step with what her readers wish to see.

Nevertheless, her decision to take on the top fashion houses has been hailed as a positive step by campaigners and by Baroness Kingsmill, who headed the Model Health Inquiry in 2007 for the British Fashion Council.

It came after some increasingly fraught discussions in the magazine over arrangements for cover shoots. Fashion designers typically base their collection around a model they have hired to wear the garments on a catwalk. The same-sized clothes are then sent to fashion magazines for photoshoots. Six months later, the clothing hits the shops — in standard sizes.

The smaller samples had forced editors at Vogue into the curious position of having to make their models look larger. Ms Shulman told The Times: “I don’t want to be too specific about it, but it was very recently. I found myself saying to the photographers, ‘Can you not make them look too thin?”

The problem had become more pressing in recent months. “Quite often I hear the fashion editor say when talking about one model or another, ‘I don’t think she will fit the clothes’. Some of the girls she was talking about . . . were already very thin.”

Supermodels such as Linda Evangelista and Naomi Campbell, who have returned to fashion magazine pages in recent years, could not fit into many of the samples. Newer models, such as Daisy Lowe, were also not thin enough to fit samples they were sent.

“Look at these young scene girls,” she said. “The Geldof girls, Alexa Chung. They are not the kind of thin that the girls we need to use are. Daisy Lowe is a good example. She wouldn’t fit into these samples.” Robin Derrick, creative director of Vogue, said: “I spent the first ten years of my career making girls look thinner. I’ve spent the last ten making them look larger.”

Sophie Baudrand, fashion and celebrity booking editor, said that in recent months she had been required to find models who were 5ft 10in but had 23-in waistlines.

Ms Shulman sent the letter to all the world’s major designers. Domenico Gabbana, John Galliano, Stella McCartney, Alexander McQueen and Donatella Versace were all sent the missive noting her concerns. Designers at Burberry, Balenciaga, Valentino and Lanvin were also sent the letter.

She does not believe all designers are culpable, but said: “People say why don’t we use size 12 models. I can’t if I’m going to do any new Prada, Dior, Balenciaga or Chanel collections.”

She sent the letter at the end of last month and so far has had only a few responses, mainly from British designers. “They have mainly said yes, they agree, but their sample sizes are perfectly reasonable sample sizes.”

Many fashion houses contacted by The Times yesterday declined to comment, some wished to know who else was ready to respond before answering. A spokeswoman for Christian Dior said: “Our position on the size-0 debate has always been quite clear, given that Dior has a well-known policy of casting healthy-looking models in all our activities.”

Chanel and Versace could not comment on the issue and Alexander McQueen and Muiccia Prada were both unavailable for comment. Paula Karaiskos, of Storm Models, the agency that handles Kate Moss, said that bookers at the agency felt that “by and large there are fewer designers who make smaller samples than not.”

She added: “There has been a trend for very skinny girls but we are not promoting this. If you look at a lot of the more in-demand models, and a lot of the actresses, there is a growing trend at the moment for a more healthy and even more voluptuous look.”

However, Eleni Renton, founder of Leni’s Model Management, which handles Nathalie Suliman, the curvacious underwear model used by Marks & Spencer, said Ms Shulman was “absolutely right”. “There are so many people now who don’t seem to be designing for women. They are not making clothes for the female body. They are creating female clothes for a man’s body. No hips or bust. It’s absolutely preposterous. I think designers are responsible.”

Back at Vogue, Ms Shulman links readers revulsion at “angular models” to the recession. “We have done a certain amount of research on images,” she said. “We find people reading the magazine don’t want to see very thin girls. I also have a feeling that in the current climate, people actually want models who look more reassuring. I don’t think designers have caught on.”

She does not believe regulation is the answer but she hopes that her letter will spark a debate that shocks designers into creating larger outfits for the catwalk and the magazines.

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