Shortly after this, however, Moss's look became associated with something more sinister: heroin chic and the glamorisation of anorexia. It marked one of the low points in her career. Moss has tried to distance herself from both harmful associations. "I had never ever taken heroin," she has said.

But her infamous quote in 2009 to trade publication WWD.com that her motto was "nothing tastes as good as skinny feels" didn't help her reputation as a bad role model. In a rare interview with Vanity Fair in 2012, she appeared to blame those around her for her bony frame in the 1990s by explaining "you don't get fed".

For the past 10 years her appeal has centred on her "get-the-look" paparazzi-friendly wardrobe and the perception that she is having the most fun in the world, whether it is cackling on the beach in a bikini with fag in hand or emerging from a VIP party with her rock-and-roll blonde locks perfectly dishevelled.

Shulman believes the secret of Moss's continued relevance is "probably glamour". "I think she is a glamorous person. I always thought glamour involves an element of unpredictability and unruliness and I think you can apply that to Kate. It isn't simply that she is beautiful, it is that she is glamorous as well."

Her glamorous rock-and-roll reputation came briefly unstuck in September 2005 when the Daily Mirror ran photographs of her apparently taking cocaine. She was never charged and although she lost contracts initially – Burberry, Chanel and H&M dropped her after the scandal – both big designer brands have since employed her. Neither her earnings nor her reputation suffered in the long term.

Critics of Moss are hard to find among those who know her. Off the record, some insiders claim that she can be "quite spoilt" and, more tactfully, that "she knows what she wants". But the Kate Moss circle is tight. Loyalty and silence are the watchwords among her friends. Tellingly, she still hangs out with many of the same friends and colleagues she has had throughout her career – publicity agent Fran Cutler, hairdresser James Brown and disgraced designer John Galliano.

The latter designed her wedding dress for her marriage to the Kills musician Jamie Hince in 2011 when the rest of the industry was keeping him at arm's length. Doukas remains her agent, but as a spokesperson explained: "Sarah is very involved with managing Kate's career, but she rarely discusses Kate in public." Moss's loyalty is repaid by their confidentiality. Shulman says: "You talk to her friends and they adore her. I can only imagine that her loyalty to them plays a part in that."

On-the-record Moss talk is easier. Makeup artist and long-time friend Charlotte Tilbury has said of Moss's face. "She is a makeup artist's dream with her killer cheekbones, heart-shaped lips and incredible almond-shaped eyes." Photographer Tim Walker says: "She has such a joy for life. You have never met anyone with such a sense of living 100% in the moment." Meanwhile, Jacobs describes her as "not only a fashion icon, she embodies the spirit of London. She is a woman of incomparable style." Shulman says: "Something about her is iconic. I hate the use of that word, but Kate is one of a few people that it genuinely applies to."

The fascination with Moss is destined to continue with industry watchers and fans looking forward to vicariously enjoying her 40th birthday party and to seeing what her one-off collection for Topshop will be like this spring. Insiders are already proclaiming it to be better in quality than the 2007 collection. But as ever, it will be her actions more than her words that keep us in thrall. Tantalisingly, Shulman says, "she doesn't talk in public but she talks non-stop in private. She is garrulous and cracks jokes non-stop. To be so disciplined and restrained about saying anything in public is such an interesting mix."

Moss says she is not ready for full disclosure, with no autobiography coming in the short term. "Not until I'm, like, 105. Because you can't get a good book unless you're going to spill the beans, and I can't spill the beans … not for a long time."