Eccentric, engaging and inspiring — and still at the top of his game at 71 - Paul Smith is appearing at Esquire Townhouse on 13 October for a conversation with Esquire Editor-in-Chief Alex Bilmes. Buy your tickets here.

Smithyland — that is, the global headquarters of the Paul Smith fashion brand — is housed in a handsome, red brick warehouse on the edge of the long-gone fruit and veg market in Covent Garden. From the exterior and the smart but unshowy waiting room there is little indication of the building's eccentric owner: not his distinctive cursive signature; nor the thin, bright stripe pattern he created that became so popular he had to kill it off. Not even a rabbit, an animal that, in various forms, has been a lucky charm for much of his career and which must be doing a job because the 70-year-old Smith has clung on at the top, or near it, of a notoriously greasy pole for the best part of five decades.

The absence of branding on the building could be taken as a reflection of its egoless, don't-call-me-Sir-Paul proprietor. But, in truth, you wouldn't have to be much of a detective to work out that this is Smith's place. Behind the reception desk, there's a cabinet full of tell-tale curios: an Eddy Merckx poster, mini-robots, David Bowie memorabilia. Climb the four flights of stairs to his office — the lift, as usual, is broken — and you pass hundreds of framed photographs, many of which were taken by him or have a personal resonance. Then, slightly puffing, you are in front of the man himself: you might need a few seconds to catch your breath, but that's OK, because Smith starts talking and pretty well doesn't stop.

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Paul Smith photographed in his first shop in Byard Lane, Nottingham, 1970.

"Tea, coffee?" he asks, leading you into his office, the Nottingham earthiness in his voice gone nowhere. "Bacon, eggs, beans?"

I'm not the first visitor or journalist to have a pop at describing Smith's mancave and I'm already resigned to not quite doing it justice. There are wobbling high-rise towers of books everywhere, so many that Smith has found that the only way to keep track is to operate a micro lending library. On walls and in piles, there are artworks, many of them very valuable: a Le Corbusier painting, an Yves Saint Laurent sketch, a Cecil Beaton photograph. Bicycles are piled up, as if dumped by students late for their 9am lecture, except these machines used to belong to Bradley Wiggins, Mark Cavendish and Chris Froome. "A little girl was in here the other day and she counted 20 bikes," says Smith, wafting a hand. "But then I think she might only have been able to count to 20."

Best of all, though, is the exotic junk that Smith hoards and curates like no one else on the planet. One example: for over 30 years an anonymous fan — he doesn't even know if it's a he or a she, only that the postmark is from the United States — has been sending him odd keepsakes. They arrive unwrapped, with the stamps stuck directly on to the object, which might be a snowboard, a fluffy chicken, a ladder, a seven-foot sunflower. A recent gift that arrived was a female torso, which — important detail this — was made from bright pink plastic.

"The postman wasn't quite sure where to hold it," Smith chuckles. "And the receptionist just said, 'Oh, for Paul, right?' It's become like a performance art and it's an absolute delight in today's greedy, homogenised, corporate world. There's no demand: I love you; I hate you; I want money. Nothing. It's just a thing that somebody does."

Smith has gone serious, at least for a moment. We are meeting at the tail-end of the year, one of those murky December days when it feels like the sun has pulled a sickie and stayed home. And 2016 has been a challenging year for Paul Smith, both the man and the brand.

"Yes, it's been quite troublesome," he admits. "Obviously we have had Brexit, we've had Trump, we've had the referendum in Italy, we've had terrorism. Places like France, 30 per cent less people are going to Paris so that's a very practical problem. The worldwide recession has never really gone away. It is just that people have been in quite a lot of denial. So for us, we've got a stable-but-flat business, which is better than a lot of others out there that are not stable and not flat. And they are having to cut down staff or close shops. Luckily, we're not cutting down on staff or shops at the moment."

In this climate, the Willy Wonka-esque Smithyland — which he describes as "child-like" but resolutely not "childish" — has become something of a sanctuary from a cruel world. "We just had some people here for a sandwich at lunchtime and they were saying" — Smith exhales — "'Oh thank goodness for this office and thank goodness for this conversation because it's just so light-hearted. And so refreshing.' I had my business when there was the coal miners' strike in the Eighties and the three-day week, when you had to have a generator for the rest of the week. And I managed to always do well through these things. So, we're not going anywhere incidentally, we're very solid, it's just you're witnessing a time which is different to what you've witnessed before."

It's a grim picture, but Smith, an inveterate entertainer, never allows the mood to sink for too long. "I get to work every morning at 6am and I have this wonderful relationship with the cleaners," he says. "It's a bit of a skill cleaning in here: she puts the vacuum cleaner on blow, which you can do, you turn it the wrong way round. So she goes, 'Pffffffff!' Then she turns it to suck and collects all the dust in the air."

A lean, handsome man, Smith is the best advertisement for his own clothes: today, a denim shirt with pearl buttons and indigo chinos. Suddenly, he springs to his feet, with the zeal of a lepidopterist chasing a rare species with a net. "So she goes 'Pffffffff!' And then 'Ckckckckk!'" It's a very funny little skit, as he leaps around the room trying to tame the nozzle of an imaginary vacuum: who knew Paul Smith, knight of the realm, was such a clown? "And it works!"

Even if you only have a passing interest in fashion, the story of Paul Smith is a fascinating, and perhaps unrepeatable, business case study. How did a one-man brand turn into a global mega-empire with a turnover, in 2015, of £192m? How did someone who started in a windowless broom cupboard in Nottingham grow that into 39 directly owned shops, 180 franchises in 60-odd countries and a scarcely credible, looks-like-a-typo 250 stores in Japan? And all of this has been achieved with cursory tailoring experience, dyslexia and while still retaining a majority stake — a rarity in the industry these days — in the company that bears his name.

Smith opened his first store, the grand-sounding Paul Smith Vêtement Pour Homme, in 1970 in his hometown, when he was 23. It didn't feature his own designs yet, but it already had some elements, in miniature, that would later become his trademarks. While most retailers aim for a fixed sales return per square foot, Smith's boutiques have always been more focused on creating a "special feeling". In its original incarnation, this meant offering records and magazines alongside the clothes. The ambition has since increased significantly: at No 9 Albemarle Street in Mayfair, his flagship store, there's a room with 26,000 dominoes covering the walls, mainly to stimulate conversation between staff and customers.

"The owners of both Colette in Paris and 10 Corso Como in Milan have both independently said that our way of running a shop was the influence for their shops, which was having not just clothes," says Smith. "So I suppose, without realising it, I was the absolute pioneer of all that, really."

Smith started making his own clothes in the mid-Seventies. Aged 21, he'd met a girl from London, Pauline Denyer, a Royal College of Art fashion graduate five years his senior. She taught him sewing and pattern cutting on the long pine table in their flat, and he supplemented these lessons with night-school classes from a man who happened to specialise in military tailoring and ceremonial dress. These two approaches fused Smith into an approach often called "classic with a twist", though I prefer Smith's description: "no-bullshit clothing". Along with Giorgio Armani, he led the trend to relax the lines of the suit in the Eighties, and he is also credited with re-popularising boxer shorts.

Like many readers, I'd guess, Paul Smith has been part of my wardrobe for all my adult life. It started with the little things I could afford, mainly boxers, and hand-me-downs from my older brother. Latterly, Smith's clothes have proved timeless and near-indestructible, better-made than makes any commercial sense. I have a red and black checked shirt by him that must be the oldest, most-worn item in my wardrobe. It's not crazy-exciting to look at, but it has horn buttons and subtle contrast cuffs. Smith seems to know intuitively that while most men don't necessarily want others to comment on what they're wearing, that doesn't mean it should be boring. Or that it shouldn't feature details that only they know about.

When Smith met Pauline, she already had two young children, and together they had two Afghan hounds and a pair of long-haired cats. (Smith jokes that he and his pets were hard to tell apart: flowing locks, big schnozzes.) That sounds like a lot of responsibility for someone who left school at 15 with no qualifications, I suggest.

"Well, I did anything that came along to earn money, which I think has given me the skill of doing lots of things," he replies. "I was a racing cyclist from the age of 12 to 18 and you learn that you do have a competitive spirit and you learn about teamwork, which has helped me enormously having 180 people in this building. I don't think I'm really competitive but I do have a survival instinct, which is, 'Well, we'll just work it out then.'"

In a tough time, this resilience has been called on again. "Paris has got a lot less people, so let's try and sell to more of them online, which is what we've done," says Smith. "It makes you dig deep. In cycling, they always say you dig deep when you're feeling tired and during the 2008 recession and things like that, you think, 'That's not doing so well, so let's try…' Then we opened three shops in India, for instance. So you just sort of work it out somehow."

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On the runway with the Paul Smith models during Paris Fashion Week menswear SS \'17 collections,.

For a man who turned 70 last May, Smith is certainly not resistant to change. His collections have always been known for their almost-ADHD variety of ideas: perhaps 1,600 items in a season, produced in small runs, whereas other designers might typically design, say, 600, but in much bigger quantities. The goal, he always said, was that his customer should never go into a pub and see someone wearing the same shirt. But in December 2015, Smith announced that he would be streamlining his business — in line with similar initiatives from Burberry and Marc Jacobs — from 12 offerings to two: Paul Smith and the more affordable PS by Paul Smith; Paul Smith London and Paul Smith Jeans were among the lines either trimmed or incorporated. The move came following results that showed the group turnover was down by 8.4 per cent, though e-commerce revenues were up 12 per cent.

No one is about to call Smith cut-throat, but he is clearly capable, when needs be, of taking hard decisions to secure the future of the business. I remind him of an old quote from his wife Pauline that hints at a steely quality to the jovial, avuncular designer. "We have always described our projects as 'keeping plates spinning'," she said in 1995. "Has Paul ever dropped a spinning plate? No. But he has, on rare occasions, disposed of one, usually due to mistrust. Then the side of Paul that people rarely see is exposed."

Smith laughs, "Ho-ho, that's very good. I didn't know she'd said that."

Does he have a temper? "No, not at all," he replies. "I don't think I've ever lost my temper, probably twice in my life, it's very unusual. Pauline and I never argue at all and we've been together since 1967."

The famous Paul Smith stripe is an example of his pragmatism. It was never meant to be a recurring feature on his clothing and accessories. In fact, Smith was always wary of such things: he doesn't do T-shirts with his name written on them ("I've always worked hard at no-brand," he says). But the stripe sold so well he had to bring it back the next season and then the next and then the next. Before he knew it, it was ubiquitous on boxer shorts, wallets, even his carrier bags. So, about three years ago, he dropped the stripe entirely from his designs.

"It cost millions of quid to do that," Smith concedes. "But we had to be brave. Isn't there that funny expression where you have to go backwards to go forwards? Something like that. Over the years some of the decisions I've made have been not that wise and probably some of the staff would think, 'Oh gosh, I wish he'd not done that.' I'm not autocratic and I do try to get opinions, but at some point you have to make a decision, because you can't keep beating around the bush. You have to say, 'We're stopping that for the time being. And let's think about it.'"

The stripe, modestly redesigned with a nod to expressionist artists such as Frank Auerbach, has now returned and appears sparingly on a handful of items in the current collections. "We've taken a breath and we're slowly introducing it again," says Smith. "If you have something that is too popular, you find eventually the young person comes up who is searching for their own identity and doesn't want something that was worn by the guy who reads the sports news or by their older brother or their dad.

"In your life, you must probably have 20 bands, 20 restaurants, 20 fashion labels that were important when you were 18 and either don't exist or they're less important now," he goes on. "We'll all experience how fickle it can be. So, by just keeping your head and keeping very solid, that's why, luckily, we're doing OK."

A week after our first meeting, I return to Smithyland to meet Smith at the end of the work day. Most evenings, he drives his Mini Cooper from Covent Garden to his home in Notting Hill, stopping in at No 9 Albemarle Street to check in on business and show his face. Tonight, I'm coming along for the ride. He bounds down the stairs at his HQ, pauses (for reasons best known to himself) to lie down and stretch out his six-foot-plus frame on the reception counter and then we're out, like Bruce Wayne becoming Batman, through a back door and onto the road.

At a time when bricks-and-mortar stores are being overtaken by online sales, Smith's decision to expand No 9 Albemarle Street, an opulent refit completed in September 2013, might seem like an odd one. Why did he do it? "I adore shops, I'm a merchant," says Smith. "I like people."

We whizz along narrow streets, parallel to the Strand. "This is a little rat run," Smith commentates. "Of course, when I did 'The Knowledge'… I was a taxi driver for 25 years — but only at the weekend!" He laughs and toots his horn at no one in particular.

Smith is sincere in his affection for shops. There can't be many big-name designers who pace the floors of their own establishment, but he can be found most Saturdays at No 9 Albemarle Street for at least a couple of hours. "You respect the people who pay your wages," he explains. "So many designers build up a reputation and then surround themselves with subservience in their ivory towers, with their chauffeur-driven cars. And they have a great success for eight years or something and sadly start to go into decline. So by going out there, a) I love it and it's nice to meet your customers. And b) you learn as well: 'Why don't you do big-fitting suits?' Or, 'Why don't you do long-fitting?'"

He spots a parking space and swings the Mini in. "Neither of those things are true incidentally," Smith says.

A true destination experience, No 9 Albemarle Street channels the spirit, if not the chaotic mess, of Smith's office. Clothes are perched on a slab of 250-year-old burr oak from Devon; shoppers gawp at a set of resin- cast fingers attached to a battery made by the mechanical sculptor Nik Ramage. There's a one-off bicycle from Mercian in Derby that has been sprayed in multicolours and is priced at five grand, a figure, Smith admits, set because part of him hopes no one will buy it and he will be allowed to keep it.

Striding into a Paul Smith shop with Smith himself is a surreal experience. He must be confident in the quality of his products, I say, because otherwise he'd endlessly have customers coming up to him to complain. "You'd get a black eye!" he replies. "But people will say they bought shoes 20 years ago and they are still wearing them. They are too well made!" Smith might not consider himself a celebrity, but the double-takes from Japanese tourists are especially pronounced. He has visited Japan more than 100 times since 1982 and the country accounts for nearly half of his company's sales.

"People always ask why I'm so popular in Japan and I always cite the rubber chicken," says Smith. "When I first went I was on my own and it was 18 hours via Anchorage, economy class. You'd go for two weeks and you'd get really tired and hardly anyone spoke English. So you'd be in a meeting and sometimes, if the timing was right, I'd just go into my bag and go, 'Bleurgh!' and pull out a rubber chicken. They'd go, 'Whooor!' Then of course, the next time they'd want to know where it was. It was one of those things where it just breaks the ice, makes people relax and makes people realise you've got a sense of humour. And they could never knock it because I was always so correct.

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"I'm the king of bad jokes," he goes on. "I'm very polite, very well mannered, very correct, but odd and unfunny and sort of cheeky; sometimes a bit theatrical. I remember sitting down for a breakfast or something at Downing Street and I had Jony Ive from Apple next to me, and he said, under his breath, 'Paul, no mucking about, right?'" Smith laughs, "Because he knew that I'd probably get a napkin and pretend to sneeze or something. Do something funny."

It's almost 6pm and a day that began, as it always does, with a swim at the Royal Automobile Club at 5.15am is starting to wind up. These are long hours — for anyone, let alone a septuagenarian — but Smith wouldn't have it any other way. And, even though these are complex, challenging times for his business, and for all companies in the fashion industry, one suspects that he will be able to pull a rubber chicken or two out of his bag when he most needs to. You wish him well, too: in these often bleak times, it is heartening to know there are still people who take the business of whimsy and silliness very seriously.

"I do put the hours in," he says. "There was a guy I liked on television years ago and somebody said, 'How well you've done with your career.' And he replied, 'I admired this chap once and I thought, I can't be better than him but I can work longer hours than him.'" Smith guffaws and heads for home and a quiet night in with "the missus". "So I thought, 'I'll try that!' Just work longer and harder than everyone else. Get more hours in and see if that works."

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Paul Smith photographed for Esquire in his Covent Garden office, London, December 2016.