Amidst the ephemera of London’s annual style showcase stands a designer whose career has endured. Paul Smith tells Carola Long why 62 is no age to be thinking of retirement

London Fashion Week opened yesterday and anyone with an interest in the industry can expect to see British design talent trumpeted in newspapers and on websites across the globe. Amidst the search for the next big thing, one name stands out on the schedule. Sir Paul Smith, who will show his collection on Monday, is unrecognisable to some of his customers – to the extent that he has even been known to work in his own stores in the UK without being identified.

But his name, his designs, and his signature stripes are so renowned that they have made his label a prestigious household name.

The label has 100 shops worldwide, a total of 1,291 stockists and a turnover of £345.9m last year, up 17.4 per cent on 2007.

While much of the high street struggles, and designer labels lay off staff, the Paul Smith shopping website is up 64 per cent on last yea.

In Smith’s own outlets, rather than wholesale, takings in January were “unbelievably up on last year”.

So much so, he says, that “I’m too embarrassed to say how much we were up, because it sounds like showing off.”

He is particularly successful in the Japanese market, which accounts for half of his sales. Seated in his objets d’art-stuffed Covent Garden HQ, he recounts various tales of being mobbed in that country, where he is a cult figure whose face is as familiar as his suits or shirts.

There was the time that “a small group of fans grew into a throng of 500” and Smith had to stand on a wall and call a car to collect him by way of escape. On another occasion he had to flee a shop by the fire exit, “like in that Beatles film”, because of a crowd. Then there are the fans with peculiar autograph requests... “I can’t tell you some of the things people have asked me to sign,” he says, “but there have also been legs, arms, sweaters, jeans, Mini Coopers and a Bentley. It’s mad.”

“Mad” and “bonkers” are words Smith uses several times, equalled only by the frequency with which he refers to the concept of “balance”.

His eccentric streak is matched with a regimented discipline which has allowed him to build an empire which now encompasses everything from men’s and women’s clothes to luggage, perfume, calculators and – how very British – a stripy cricket ball. Years ago the luxuriant-haired designer summed up this duality in the phrase, “classics with a twist”.

He describes his upcoming Autumn/Winter 2009 show on Monday as, “very Paul Smith, just the mad mix, that’s really what I specialise in”. He explains: “So there will be an old army raincoat over an exquisite printed floral ball-gown.

“It’s got a strong couture feeling, and also a big colonial influence,” he says. “The show was based on some photographs my friend took of Darjeeling which look so English. There was a strong [British] army presence there, so the collection is a bit colonial, slightly military, a bit vintage, quite a melange of things, quite a lot of army colours, little visual jokes and special fabrics.”

Smith, who was born in Beeston, Nottingham in 1946 – he has since designed a uniform for a school there – is renowned for immaculate, traditional British tailoring, updated with quirky details such as a vibrant lining. The pinstripe jacket he is wearing today with a cowboy shirt and jeans is lined with a multicoloured blob pattern. Then there was the naked lady embroidered on the cuff of the suit famously worn by Tony Blair. Smith is fond of vibrant prints, not just his famous multistripe but also bold florals on shirts for men and women, as well as quirky details such as Mini Cooper-shape cuff links or a trompe-l’oeil T-shirt printed to look as if there is a cardigan over the top.

Humour is also essential to Smith’s modus vivendi; he has been known to suddenly produce a rubber chicken in the middle of business meetings.

He didn’t learn his craft at fashion college, falling into the business by accident. After leaving school at 15 with no qualifications, his dad marched him into a clothing warehouse in Nottingham and made him take up a job running errands.

Initially, the only task that engaged Smith was the cycle ride to and from work, and he had dreams of being a racing cyclist. However, when an accident ended these ambitions, he threw himself into his job, befriended students from the local art college and developed an interest in fashion. When a college friend decided to open a fashion boutique in Nottingham, Smith became its manager, and in 1970, encouraged by his wife Pauline (the “unsung hero”), he opened his first shop in his home town. Smith showed his first menswear collection in Paris in 1970, opened his first London shop in 1976 and the second three years later.

More shops followed, in the US, Paris and Tokyo, and in 1993 Smith launched his first womenswear collection in response to ladies borrowing their boyfriends’ or husbands’ Paul Smith garments. Other notable points in his career include the launch of glasses, luggage, fragrances and furniture – and a knighthood in 2000.

Another landmark was the first womenswear show at London Fashion Week in 1998. Smith doesn’t think our fashion week has changed much in its 25-year history: “It’s still got this creativity and usefulness. Luckily there is this anchor of established people like myself and John Rocha, Betty Jackson, Nicole Farhi and Jasper Conran, but it’s also very much about nurturing young talent.”

Smith feels sufficiently laid-back about his show on Monday to be catching a Eurostar to Paris for a private view of Yves Saint Laurent’s art collection this weekend. “I was invited by Pierre Berger,” he says, “and Pauline plans to wear her couture YSL Le Smoking suit – the last couture version YSL ever made.”

He is leaping round his office to explain the provenance of the myriad items on display, like a caffeine-fuelled curator. Amidst the organised chaos there is small wooden chair covered in stamps – one of several items that Smith regularly gets sent, unpackaged, by the same anonymous person – photographs by Marc Quinn, a Banksy, a gold rabbit statue, books on design, and a football made of bread by his favourite Paris baker, Poilâne.

Smith is absurdly modest, saying that he credits his success to the balance between different forces at work in fashion industry, such as creativity and commercial viability. “I started working in a shop at 15, so I understand that the VIP is the customer,” he says. “Unfortunately a lot of mystique surrounds the world of design, in the fact that a lot of designers get sucked into the world of theatre and think all the clothes should be very attention seeking.”

He concedes: “Of course you do need what the press call ‘directional’ clothes for the catwalk; but behind that, or within the collection, there needs to be clothes that people want to buy – not just a coat with three arms.”

Smith’s modus operandi provides a template for up-and-coming designers. He has kept his licensed products such as perfume and spectacles under strict control. He has resisted offers to buy the company outright, although two years ago he sold 40 per cent to Itochu, his principal licensee in Japan. “The business has grown very gradually over the years, we have almost no borrowings and we own a lot of our shops,” he says. “I wanted a business with longevity.”

At least part of the reason that Smith has achieved this goal is his hands-on approach.

One might not expect to find a designer of his calibre pinning trousers or helping customers in one of his own shops, but that’s how Sir Paul Smith often spends a Saturday afternoon.

“It could be the Notting Hill Gate or Paris store,” he says.

“I wander around and if a customer needs me than I give them some help. A lot of them don’t even know it’s me, because I’m quite a private person.” Sometimes this market research method can get too intimate. “I was pinning a pair of trousers on an American gentleman,” Smith recalls, “when he started talking to his wife and saying, ‘Hey Jack knows Paul Smith, he’s supposed to be a really nice guy.’ I had to slope off after that.”