Out of sight, not out of mind: Celebrating two decades of Martin Margiela magic

To those who paddle in the shallow end of fashion's infinity pool, the murky depths of conceptual fashion may seem far off and unapproachable. The best way to describe Martin Margiela, then, is as a gentle undercurrent, whose influence works its way from high-end catwalks to high-street pavements by an almost unnoticeable process of diffusion.

So you think you're fashion-forward in your shoulder pads this autumn? Margiela showed them for spring 2006. Ditto high-waisted skirts, capes, leggings and almost any other mainstream fashion item du jour you'd care to mention.

The Belgian designer's first collection, for spring/summer 1989, included a leather butcher's apron reworked into a seductive evening gown, and an old tulle dress, which he had remodelled into several sharply tailored jackets. Known for his deconstructionist take – often using traditional lining fabrics as outer layers, and leaving hems and seams rough and trailing – much of Margiela's magic comes from working in unexpected media and reinvigorating what most would see as detritus.

"I think that people today don't realise how it was," believes Bob Verhelst, who has worked with Maison Martin Margiela (as the fashion house is known), and curated the anniversary exhibition of the designer's work at the Mode Museum in Antwerp earlier this year. "After the first show, everybody came out and nobody spoke. Margiela had recalibrated the sewing machines so the overlock was not cut automatically, but was left dangling from the seams. It was confusing, as everybody knew it was ' strong, but they were not sure if it was good. And then we saw the next season that a lot of people changed direction immediately, and the influence was undeniable."

In September 2007, the International Herald Tribune fashion editor Suzy Menkes and the designer Marc Jacobs had a spat when her show review claimed that Jacobs' work was too reliant on Rei Kawakubo of Comme des Garçons, and Margiela. He was unapologetic, and told Women's Wear Daily: "I've never denied how influenced I am by Margiela or by Rei Kawakubo, those are people that inspire my work. I don't hide that. Everyone is influenced by Comme des Garçons and by Martin Margiela. Anybody who's aware of what life is in a contemporary world is influenced by those designers."

Yet Margiela, known as "fashion's invisible man", is not a designer who takes a bow at the end of his shows. He doesn't give interviews, very rarely has his picture taken, and any correspondence that journalists or buyers enter into with his atelier is plurally signed "Maison Martin Margiela". In an industry that relies so heavily upon recognition, contacts and relevance, he is an anonymous anomaly, but to those who know fashion, his is practically a household name. In fact, it is a household name, given that it now stands only for his work and his company.

He has many reasons for his intense privacy: first, he aims, by suppressing himself, to focus attention on his designs, however confusing or outré they may be, which is why he also often sends models down the catwalk backwards or with their faces covered. In the current cult of celebrity designers, this seems a watertight argument. Having gauged reaction to lines by Kate Moss, Victoria Beckham or the Olsen twins, who's to say whether consumers now buy pieces because they like them or because someone famous appears to like them?

That's not to reason, of course, that buying Margiela isn't buying into a movement, and this is another reason for the designer's anonymity as well as his eponymity: you're being let in on a delicious private joke. Those who know Margiela's clothes know who wears Margiela's clothes – the only identity now left to this man comprises four diagonal white stitches, arranged in a square, on the back of a jumper, a dress or the outer side of a scarf. It's where the labels are sewn in, and it's the essence of Margiela's methodology: he's the anti-designer with an anti-designer label. Margiela perpetuates a system of inconspicuous consumption.

That label celebrated its 20th anniversary last year with a catwalk presentation that featured a walking birthday cake and an oom-pah band surrounded by Margiela's lab-coated assistants. It was, if not a greatest hits collection, certainly a resurrection of some of the pieces that made the biggest waves in the fashion pool. And a selection of these one-off pieces have just gone on sale on the shopping website yoox.com.

His wig jacket, for example, is an ironic rendering of a super-luxe fur coat in brown acrylic hair, which took 51 hours to sew together. The equally tactile plastic-tags jacket is made from thousands of those irritating needles that hold labels on to new clothing. And the disco-ball top, an asymmetrical armour vest, is made from hundreds of mirror squares assembled around the body. Each of these pieces comes from his "artisanal" range, one of 11 carefully codified lines that the house produces, each assigned a number, all of which make up the esoteric numerical system seen on Margiela's otherwise plain white labels. His flagship store in Brussels is painted entirely white and an explanation of each numbered range is stencilled on to the side of the building; it is a place of pilgrimage for many fashion followers.

Margiela stores can be found in slightly weather-beaten, reclaimed buildings far from the fashion streets of the world's style capitals. The original London shop was in Mayfair's Bruton Place. The walls were white- painted bricks. The products and displays were scarce and the tills were like supermarket check-outs with metal chutes which your sartorial alimentation slid down before being bagged up by one of the many lab-coat-wearing assistants. It simultaneously took the glamour out of buying designer clothes, while injecting the process with humour and quasi-ritualistic pomp. The new shop, just around the corner in Bruton Street, is a challenge to find and, on entering, the space itself is a blizzard of silver and white – it is, the Maison says, a "found object".

Entering any of the Margiela stores worldwide is an experience rather than a shopping trip. Likewise, wearing Margiela is much more than quickly trying something on. There are often dozens of sleeves to negotiate, for a start, or you find that a jumper is supposed to be worn with the neck around your hips perhaps, or the lining becomes a Mobius strip of silk and is somehow the outer layer too. Such geometry requires more than a changing-room, more than a mirror, more than one pair of hands.

The company was bought by Diesel in 2002 and the cognoscenti were sad to hear the rumours that Margiela himself had stopped designing after the anniversary show. Although the news was not confirmed until recently, several rather wobbly collections were proof that he was no longer in the building, and there are whisperings of fellow Belgian Raf Simons, currently at Jil Sander, and acclaimed new talent Haider Ackermann being courted for the job. But both are understood to be nervous, because of the anonymity clause that comes with the territory. "We appropriate, we do some vintage," the fashion demi-god Azzedine Alaia once said. "Individual vision no longer exists. Margiela is the last one."

Proceeds from the sale of Maison Martin Margiela's artisanal pieces on yoox.com will go to the Rosa Spier House in Holland, a non-profit organisation that offers housing to retired artists and academics