Style and substance: The prime of Miss Jean Muir

When the sale at the Jean Muir shop in Conduit Street, central London, closes on Friday, so will the 41-year-old fashion house. It's unlikely that the teen shoppers at H&M, just around the corner, would even recognise the name.

Nor would many of the logo-hungry tourists at the Louis Vuitton flagship on adjacent Bond Street be familiar with the signature matt black and navy jersey dresses - although they might, unwittingly, wear clothes that use Muir's technical innovations of the 1960s and 70s.

Jean Muir, who died in 1995, was one of the greatest designers Britain has produced. Following her wishes, a design team have, for the past 12 years, produced collections according to the understated codes that Muir believed in. She was a staunch minimalist and had a fearful reputation. Preferring to be addressed as "Miss Muir", she had a deep mistrust for the hype and glamour that fashion feeds on. She preferred the term "dressmaker" to "designer", believing that that latter underplayed the craft of her trade. "Clothes aren't fun and games," she once said, "This isn't a silly, frivolous business. I hate the word fashion. It doesn't mean anything."

To those in the know, hers was one of the most significant names in British fashion. "I adored her things," says Manolo Blahnik. "She knew how to cut jersey like nobody else. When I first came to London in the 1970s she asked me to make her shoes. She knew immediately what she wanted. She had an extraordinary mind. My first impression was of a birdlike creature with a very un-birdlike force."

Jean Paul Gaultier, Issey Miyake and Giorgio Armani are among the global fashion stars who have professed their respect for her brand of pared-down design. Burberry's creative director Christopher Bailey is also an admirer. "Her design had real integrity," he says, "she never veered away from that vision. I never actually met her, although I would have loved to, but I respect the grace of her design. It was minimal but still very tactile."

Such was her reputation that after her death, at age 66, her widower Harry Leuckert was able to forge on with the business. Never bowing to trends, the studio of designers that Muir had assembled in the Nineties continued to produce immaculately cut jersey dresses and sober separates. The house's fashion shows were rather genteel affairs where journalists sat alongside customers - ladies of a certain age, true, but never suburbanites - around a small catwalk in the flagship store.

Born in London to Scottish parents in 1922, her gift for drawing was obvious from a young age. Rather than go to art school, though, Muir began her career in 1950 in the stockroom of Liberty on Regent Street. It was at that store that she "learnt the business from A to Z". Attending fashion illustration evening classes at St Martins School of Art (and modelling for fellow students for extra cash) she then went on to join Jaeger, becoming head designer in 1956. Her first solo venture was Jane & Jane, formed with Leuckert as co-director. Vogue called Muir "one of the new young names that are giving the Sixties an accent all their own".

However the pair did not own the label, so in 1966 she and Leuckert formed the fully independent Jean Muir Ltd. Looking back to the 1930s for subtle inspiration, her spare style was tempered by the feminine crepe or jersey fabrics she favoured. Her clothes were sold in department stores around the world. "She was in Bergdorf Goodman, in New York, it was very influential," recalls Blahnik, "I remember hearing that Lauren Bacall was told, 'Miss Bacall, would you like to pick your dress now?', That was Miss Muir's power at the time!"

Although she never courted celebrity, Muir dressed Maggie Smith and Judi Dench, the sculptor Elizabeth Frink and Joanna Lumley, who was a house model. Diana Rigg's infamous catsuit for The Avengers was also a Jean Muir design. Even today, vintage Jean Muir, is still highly prized. "We always love a Jean Muir dress. It's one of our perennials because they are just so identifiable," says the Los Angeles vintage dealer Cameron Silver. Sienna Miller, Winona Ryder and Chloe Sevigny are among those who collect 1970s Jean Muir.

But while her fans were legion, Muir never achieved the financial success of other big Paris or Milan houses. An expansion into menswear in the 1980s was not successful, and neither was a sale of 75 per cent of the business to an outside investor in 1985 - Muir bought back the share in 1989. "My business is a personal business, and it's better being owner-driven," she said at the time. Like all the most successful designer brands, it was impossible to separate the clothing from the individual outlook of its creator.

Jean Muir died in 1995 from breast cancer. She had suffered from cancer for two years but had told no one but her husband. Soon afterwards, it was announced that it had been Muir's wish that the company continue after her death. Yet fashion commentators say that without her formidable leadership the house then lost its edge.

It is testimony to the timeless appeal of her designs, however, that the company continued to sell in department stores including Harrods. A flagship was opened in 2004 at a prime site in Conduit Street. Leuckert recently described the boutique as "exceptionally successful". Last autumn a grand 175-page coffee table book, Jean Muir: Beyond Fashion was published and the company's sales and marketing director, Sinty Stemp, said at the time there were plans this year to open a second store in New York. In December the industry publication Women's Wear Daily described the business as "thriving in a low-key way". The most recent reported sales figure was £2.5m in 2005. Then in January the company released a statement that an "orderly wind down" would make the current spring/summer collection its last.

This week's closure is not a case of a company forced to close for want of any other option. Leuckert's reasons for shuttering the house would appear to be rooted in principle - not something often found in an industry that usually prefers cash to ethics. He said the Muir would rather her namesake label be closed down than taken over.

"It is sad, but I think this is the way Jean would have wanted it," he says, "I have, of course, had other offers but I do not want Jean's name to fall into the wrong hands and be misused. That would be horrendous and she would have hated it. I believe there is a virtue in quitting while we are ahead and keeping her name untarnished."

"Wrong hands", Steineke says, would be those "who would exploit [the brand] by making a mediocre product," - by downgrading the label into a less expensive price bracket. "As sad as it is, I do admire that," says Bailey of Leuckert's decision. "It would be very easy for them to sell out, and the fact that he won't shows for me a real respect for Miss Muir's work."

It's likely that Leuckert wouldn't have been short of offers for the company. The last decade has seen myriad defunct fashion houses dragged off the shelf for a dusting-off. But even when supported by lavish marketing strategies, high standards of production and with a young designer at the helm, the degrees of success are variable. Balenciaga and Chanel are two 1950s houses that have been transformed for the 21st century, under the guidance of two star designers, Nicolas Ghesquiere and Karl Lagerfeld respectively. Bailey's own impressive work at Burberry has also turned around that house's fortunes.

So-called "minimalist" houses, their appeal so intertwined with the single-minded approach of their founders, appear to hold the greatest challenge in the great rush to remake and rebrand. Jil Sander's fortunes, after the departure of its founder in 2001, are now improving under the guidance of Raf Simons, although it stood at the brink. For many, the jury is still out on the feminine-futuristic collections by Calvin Klein's chosen successor, Fransisco Costa. Helmut Lang was sold last year to an American-Japanese company that plans to give the formerly avant-garde brand a wider global appeal.

So while the loyal Jean Muir fan searching for bargains at the Conduit Street store this next week will miss the house's latter-day collections, its founder's legacy will remain unblemished. Which is just how the exacting Miss Muir would have wanted it.