It's Karl Lagerfeld's world, we just live in it

Karl Lagerfeld is in town – or his head is, at least. There's a huge neon light in the shape of it on the third floor of Selfridges where a pop-up shop is about to open.

It is filled with the new and exclusive Karl Capsule Collection; Karl, the affordable range for men and women; and Karl Lagerfeld Paris menswear, a more upscale affair. All of these are designed, according to the press release, to allow customers “to experience the Karl Lagerfeld world”.

Judging by the bright young crowd in front of the store's main entrance and dutifully lined up at the sides of its escalators, in anticipation of the arrival of the man himself, more than a few are intent on doing just that.

"You know, personally, I don't even think that I'm famous," says Lagerfeld, at this point in full possession of his body and comfortably installed in a suite at Brown's Hotel for the afternoon. He is due to drop in on the launch in question before long.

"I wouldn't say I was a beginner but you're only as good, not as your last show, but your next show. I can't go into a shop without people in front of the door taking my picture on their iPhones. That's very strange to me."

He will doubtless be more taken aback still, then, when he sees that the outline of his profile also graces everything from the interiors of lifts at the aforementioned department store to the T-shirts of those operating them or showing guests to the roof where cocktails are served and Alison Mosshart is DJing.

"Yes," he says. "Sometimes even I'm surprised at what can be done with my head." Surely, though, he must realise that his self-styled, always black-and-white image – from the clothes, to the hair to the dark glasses – has as much in common with a lithograph as a living, breathing, human being.

"But I didn't do that on purpose. I see myself more like a cartoon. I wanted to become a cartoon artist when I was a child. I'm pretty good at it." His skills as an illustrator are unrivalled as anyone even remotely interested in fashion will know. "But I never proposed my face [as part of the branding]. The company asked me if they could use it. I personally am too modest, if I can say that, to make such a proposition."

It must be a relief, in an age where respect for privacy is conspicuous by its absence, that people at least have the courtesy to seek permission before stamping his silhouette here, there and everywhere. "Yes. Yes. Yes. Everybody still has to ask if they can use my head… the head doesn't come for free." Whether he fully understands it, Lagerfeld is as instantly recognisable as royalty and rock stars but nowhere near as intimidating as might be imagined. And he is perfectly well-mannered to boot. "I got here two hours ago," he says, "It's fun. It's nice. One shouldn't be too difficult, no? It's the first time I see London with so much sun. It's beautiful. All those Regency buildings in the sunlight. The standard is really quite impeccable."

Although great pains are taken by his people to separate the designer's work on the line that bears his name from that of his creative directorship at Fendi and, of course, Chanel, Lagerfeld says what he wants to say, when he wants to say it. And given his long, spectacularly grand career and ability to keep up with the times, that is as it should be. And so the Karl and Karl Lagerfeld collections are "a reflection of me as a person and the others are more like an interpretation of a style. It's never mixed. Fendi never looks like Chanel, Chanel never looks like Karl Lagerfeld. I don't know how I've managed it. I think I have no personality but in fact I have three." Lagerfeld's public persona has effectively blocked any real attempts at probing over the years and the personality he speaks of is therefore communicated on a surface level. "You see a silhouette. There's nothing else to see. I remember a photographer saying to me, 'I have to spend three days with you to know what's behind the image'. I said, 'You're wasting your time; there's nothing there'."

Both Karl and Karl Lagerfeld rely on sharp cuts inspired by menswear, on a monochrome colour palette on the contemporary uniform of T-shirt and jeans and – closer still to the designer's personal style – detachable high collars and fingerless leather gloves. For his part, Lagerfeld's skinny black brocade trousers are of his own making as indeed is his tie, but his shirt is made for him now, as always, by Hilditch & Key and his narrow black jacket is Dior Homme. "But I have worn Dior for a long time," he says.

Lagerfeld's output is more diverse than any other designer's: he is responsible for everything from Chanel haute couture where money is no object to the accessible Karl. In 2004, he was the first big name to collaborate with the Swedish high-street chain H&M: he says it was that company's decision to use his photograph in the accompanying advertising campaign that made him a household name.

"I'm very much against the idea that 'commercial' is a boring word because you cannot make a collection that nobody wears. Fashion is what people wear and what they buy. I know exactly what can be done and for what price. I know what costs what and why something is expensive or affordable. That is part of my job. I think it's very pretentious to think that you are only catering to a limited group. I am lucky, though, as I have the total range."

Luck, in a world where Lagerfeld's very longevity is the exception that proves the rule, has nothing to do with it. Instead, his is the infinitely protean model that has set the standard for contemporary fashion as practised by everyone from Miuccia Prada to Marc Jacobs. As well as designing Karl, Karl Lagerfeld, Fendi and Chanel, Lagerfeld has a publishing imprint, 7L, a subsidiary of Steidl, and he is also an accomplished photographer.

"I'm militating for a 48-hour day but that's a problem, especially in France, with the 35-hour week," he says. "I have 35 hours of rest. But I'm not tired, so that's okay with me. I have the job I want and the right circumstances in which to do it. Nobody has that like I do."

If Karl Lagerfeld is blessed then his good fortune pales into insignificance as compared to that of his one-year-old cat, Choupette. "Now, Choupette really is famous," he says. "She has become the most famous cat in the world. I even get propositioned by pet food companies and things like that but it's out of the question. I'm commercial. She's not. She's spoiled to death. Obviously. "

Choupette travels with Lagerfeld to St Tropez on his private jet "in the cockpit, with the pilot, she loves looking at the sky". She has three maids whose duties include keeping a diary of all activities and taking her to the vet for a check-up every 10 days. "I don't take her," Lagerfeld says. "I don't want her to be furious with me."

And with that he's off to make a brief appearance at his own party and then back to Paris. "Choupette waits for me at the front door," he says. "She doesn't like being alone. She gets moody."