Paul Smith’s office is full of beautiful rubbish. Up in the boardroom, a grand walnut table is slowing edging over to the back wall, as a great whirring mound of kitsch, tidbits and assorted trinkets creeps ever outward. The shelves on the wall overflow with colourful knick-knacks and handmade trinkets, while flashes of pastel and neon shapes vie for attention from a pile of garments on the oak floorboards.

The back wall is covered entirely by books, while down below the window sits an encyclopaedic collection of cassette tapes, vinyl records and CDs. If it wasn’t for Paul Smith sitting calmly and impeccably in the middle of it all, you’d think you had stumbled across the manic hoardings of some eccentric, wealthy, omnivorous lunatic. Perhaps, in a way, you would have – though there is some method in this madness.

‘I’ve got the vaguely round things over there,’ Paul says, nodding at a tumult of vintage ski helmets, signed footballs and decadent theatre masks. ‘Then there’s the toys and things over here,’ he says, leaning to his right and picking up an old wooden boat in peeling, dusty turquoise paint, embossed with the words: STATEN ISLAND FERRY. ‘Just think of the ideas you could get from that,’ his eyes flickering between the stacks and piles. If you want to know how the mind of Britain’s best-loved fashion designer works, start digging.

Paul Smith’s office is full of beautiful rubbish

‘What I promote constantly to all the guys I work with is lateral thinking. Don’t go down the obvious route,’ he says. ‘In my case, I like being surrounded by unusual things.’ You get out what you put in, he says. And Paul has thrown everything in the Magimix at one point or another. ‘I’ll just reach over to a shelf and say “I mean like this”, and it could be something as obscure as an old Pink Floyd album cover, or a cycling jersey. I picked up a big pile of match boxes from Japan that we used in a meeting the other day about the design for a t-shirt.’

Finding the idea is easy when you are in Aladdin’s cave. ‘I’ve got quite a lot of mates that are writers, and they tell me about the fear of the blank page. They’ve told me how they go down to the local wine bar to have a couple of drinks and loosen their minds up a bit,’ Paul says. ‘That’s the easiest part for me. The hardest thing is actually harnessing the ideas – focusing them into a collection.’ It wasn’t always like this.

When Paul opened his first shop in 1970 – a tiny, 12-square-foot unit in his hometown of Nottinghamshire – the ideas were harder to come by, but they did at least edit themselves. ‘We were constrained by sheer necessity,’ he says. ‘And necessity is how the DNA of Paul Smith really began.’ On such a tiny budget, and in such small quantities, Paul could only afford to buy stock white shirting or a simple blue and white stripe. ‘So I’d do a white shirt and put a different colour under the cuff, because I’d think: “why should anybody buy a white shirt from me? They’ve never heard of me!” And then you start to think: “what if I do a pink button or a green button here…”’

Even the Paul Smith Multi-Stripe – a rainbow hodgepodge that flashes onto your retina’s whenever you hear the Paul Smith name – was created in a patchwork process and borne out of simplicity. ‘I just started with a piece of card, then some yarn, and I wrapped the yarn around the card, and I built up the colours – bigger, smaller, blue, green, purple with black. Then I found this pattern and thought it looked amazing!’ The playful, creative stage is just the beginning, however.

The Multi-Stripe’s enduring success is also down to his hard-nosed pragmatism. ‘Things got dangerous. As soon as you over-milk something, you’re finished. It’s going to go to the wrong group of people, or it’s going to be what your dad wore, or you’re going to have a generation problem.’ And so, at the height of the stripe’s popularity, Paul killed it. ‘We got rid of it for a year, about six years ago. It cost me masses of money, and my sales people were looking at me like “he’s lost it”. We must have lost over £2 million in sales instantly!’ he laughs.

We were constrained by sheer necessity, and necessity is how the DNA of Paul Smith really began...

‘But I wanted to refresh it. I re-coloured it slightly, and did a new companion stripe called the Artist. We re-jigged the proportions, and muted the colour palette, and now it’s back and more popular than ever.’

So where will the next big idea come from? And how will Paul lassoo it when it trots by? ‘I’m a big note maker; I’ve always got notepads, I’m taking thousands of notes.’ He shows me some scribblings in biro on the back of his interview briefing – they’re indecipherable, written at all angles. ‘This one just says “64”. I have no idea what that refers to, and I wrote it an hour ago!’

By way of explanation Paul opens up his navy check jacket to reveal a muted stripe on the inner pocket. ‘These colours come from a painting by Auerbach, so I would have just written “Auerbach colours”, then I’d go to the book I’ve got on Frank Auerbach’ – he swivels to look at the teetering library on the back wall – ‘and look at his colours. Then the colours for a collection would come from that.’ There are hundreds of notebooks in this room alone, many filled with notes from 5, 10, 15 years ago – several-lifetimes worth of collections, several-thousand warehouses-worth of clothes, just sitting there, waiting to be brought to life.

‘The collection I’m doing next year is from a book on Kabuki theatre – it’s inspired by the colours in their Kimonos and things. And I remembered a note I had made years ago that just said “Kabuki book”, and it referred to a book I’d read years before that. Somehow I found it again, and we had a collection!’ In the back-pages of each of these notebooks sits 100 more scraps of paper, cuttings from magazines, pages of old leaflets. (‘That was actually how I made my first t-shirts, back in the 60s. You’d rip something out of a magazine and make a silkscreen from it. It was all a bit like Rauschenberg. Oh – like that one over there.’ Paul points to a priceless Robert Rauschenberg print, leaning against the foot of the far wall between framed envelopes and old cycling posters.)

‘We were in Paris and I was looking at the New York Times, and there was a picture of the Pope on the cover, dressed in white, and there was a really black background behind him. It was very striking. So I just ripped it out, and I used that as the basis for one of my campaigns, and we used a black backdrop and re-created the mood with a certain lighting.’

The papacy seems to be on Paul’s mind at the moment. ‘I think it’s interesting how the Pope said recently – “I want to build bridges, not walls”. That’s a great sentence for you, for me, for everyone. Never say “no”.’ (He lifts a piece of paper to his face, covering it completely). ‘Never do that. Let’s just chat about it.’ Ultimately, it’s from these conversations – open book chats, at all hours of the day, with all sorts of people, spilling over with references and oddities like the back pages of his binders – that Paul derives the most inspiration. ‘You have to talk to people, and everyone has something interesting to say.

‘Look around this room. It comes from all over the world. You get things from a six-year-old, a 100-year-old, a student, a famous person. We had Michael Palin in here yesterday, then a band called The Lumineers the day before…’ But for all these thousands of voices and inputs, and the shrieking carnival of these shelves, there is only one Paul Smith. ‘I just make what I like, and hope somebody else likes it too.’ He crosses his legs and adjusts a red and blue sock. ‘Well – so far, so good!’

In good spirits: Cocktails at the Connaught with Stanley Tucci

Michael Murray on how everything changed at the Frasers Group

The American Issue: Editor’s Letter