Let's start with the store, number 44 Conduit Street, which on a weekday afternoon is full of Japanese teenagers, giggling into the sales racks. There are puffball skirts and drag-queeny shoes and shirts that, unless you knew they were by Vivienne Westwood, might look to an observer as if you couldn't do your buttons up; there are the beautifully cut jackets and sculpted bustiers. Towards the back of the store are the latest versions of Westwood's notorious protest T-shirts, which are protesting at this point - and without apparent irony - against consumerism. (They are £60 each, down from £95.) I Am Expensiv [sic] reads the slogan on one; and Who The Fuck Needs Art; and NINSDOL, which Westwood tells me stands for Nationalist Idolatry, Non-Stop Distraction and Organised Lying. "It's an invented name," she says. "It means have you had your universal tranquilliser today? Have you had your pill?"
Her studio is several miles away in Battersea, south London, where on the ground floor legions of staff cut and stitch for the new collection. Upstairs, Westwood smokes in her office in a blue silk smock. She is 66 and doesn't look it - doesn't look any age, in fact, and never has; it is one of her talents to be always slightly out of context. Whenever she is photographed, Westwood seems either to be flashing her crotch or pulling a face, and from this one imagines her to be difficult, to be clinging still to the legacy of punk and the notion that rudeness is the same as subversion. But there is no sign of that today. Instead, she is peering and delicate, her white skin like the underside of a crab against her livid orange hair. "Referring to my husband," she says, in a typically structured sentence, "he designs as much as I do. As a matter of fact, he designed this dress; I didn't do this dress, it's him." Her voice is like Alan Bennett's.
The husband, Andreas, is 25 years her junior and works as a designer in the studio. (We will meet him presently.) If it were up to Westwood, she would abandon fashion for the moment and devote herself to the problem of what she calls "propaganda" and "the drug of consumerism". This is her new thing. She has written a manifesto, which she hopes to present at the Hay-on-Wye literary festival later this month, to provoke a discussion on the nature of culture and the arts; specifically, to expose the sham efforts of people such as her good friend, Tracey Emin. "I thought she and Tracey were friends," one of her bemused colleagues says to me later, "but she never stops going on about how bad her art is." Westwood can't help herself. The broad message of her piece is: the philistines are upon us! And, yes, it has caused upset in her friendship group. "Definitely. Let's just leave it at that." She sighs. "My biggest criticism is how can people be so easily satisfied? Even people with talent." She sends up conceptual art as "a symphony composed on the remaining three keys of a broken piano, combined with the random throwing of marbles at a urinal".
Westwood's convictions are so earnest, so oblivious to the possibility of ridicule, as to be strangely heroic. They also make her vulnerable. The "loony" tag that once attached itself to her in an admiring way has long since become mocking. "The tabloids like me for it," she says of her willingness to say what she thinks. "But people who write features in posh papers sometimes say, 'Who does she think she is? After all, she just designs dresses.'" She gives a small smile.
The one charge that does seem to needle her is that of "didacticism". Despite the fact she was once a teacher, she says several times in the interview, "I don't want to be didactic." Perhaps it implies tediousness, or perhaps she just likes to use the word. Of course, Westwood is thoroughly didactic - it is part of her charm, to make insupportable statements ("Descartes is shit") and, when challenged, simply sniff, in a Jean Brodie-ish way and say, "The analysis is correct." Consistency, thinks Westwood, is the last refuge of the unimaginative, which is why lots of unimaginative people keep asking her about punk, when what she wants to talk about is the decline of cultural standards.
So here it is: everywhere you look, says Westwood, people are sucking up propaganda and calling it art - in galleries and museums and cinemas. She hasn't seen the exhibition of Kylie's clothes at the Victoria & Albert Museum, but from the sound of it, she says, it is exactly what she is talking about.
"I do not approve of museums trying just to get people to come in. Whistler was very, very clear on this."
"Yes. He gave a lecture called the Ten O'Clock lecture - I've got to put him into my piece - and he was completely contemptuous of popular things, and he said people should not be hassled and harried to go into museums. Leave them alone."
Westwood has enjoyed having her own work displayed at the V&A and the Metropolitan Museum of Art in New York, but that is not to say she approves of it. Clothes are to be worn, not stared at, she says, and it is entirely misguided to elevate them to the level of, say, Matisse, in honour of whom, if there were any justice in the world, people would be "sacrificing sheep".
"Real art," she says, "has been ... what's the word? Kidnapped? No, that's not it. But OK, kidnapped by business."
Fashion is not art because it is ephemeral. She is quite firm about this. You design what you consider to be the perfect pair of trousers, and then three seasons later you are required to design another pair. "It's annoying." Big claims for the symbolic value of fashion annoy her, too. Anna Wintour, the editor of American Vogue, says that you can tell as much about the world from the fashion of the day as you can from the front page of the New York Times - Westwood thinks this is just silly.
"It's not a microcosm. It's not a view of the world. It's just an item, really - more or less like the urinal, perhaps, for all I know." She pauses. "It's an expression, an applied art. It's life-enhancing. It's not culture. It's not what Anna Wintour says."
It is unusual for someone in the fashion world to criticise anyone else in it, let alone one of its most powerful figures, but Westwood enjoys a strange status - part grande dame (she became a dame in 2006), part licensed fool - and she seems to be fondly regarded even by those she contradicts. She is dimly aware of this: "What I do appreciate," she says, "is the prestige I've got from it, you see. You've got a track record." But it is not, at the moment, enough. Her aim, she says, is "to understand the world that I live in," hence the manifesto. "I've always tried to open my mouth and say something." She smiles slyly. "I disagree with everything I used to say."
Like a lot of quietly spoken people, Westwood is steelier than she is given credit for. She has advanced skills in avoiding interruption. When she senses that you are about to jump in, she furrows her brow, breaks eye contact and, without disturbing the deceptively soft rhythm of her voice, hauls on through. Those she works with seem to regard her with more respect than warmth.
Her first job after art school was as a teacher. "I was a very good teacher," she says. "Except I always liked the kids that everyone else thought were a pain in the arse. The little rebels."
She grew up Vivienne Swire, in a village on the border of three counties, Derbyshire, Cheshire and Yorkshire, and at the age of three would be sent to the village shop on her tricycle to buy bread for her mother. (She was a great one for digressions, even then: "I'd just be skipping in the street and not get home with the bread, which would have all the corners eaten off by the time I gave it to my mother.")
Her father worked in the Wall's food factory and she describes him as "very sporty and entrepreneurial. He always made money selling puppies and holly wreaths at Christmas." When she was in her teens, the engineering work at the factory got too laborious for her father and the family moved to Harrow, where her parents ran the post office.
Growing up in the north gave Westwood a confidence that she thought friends of hers from London didn't have. Of course, she says, "I thought I was stupid," but it didn't hinder her particularly, apart from in her choice of men: she always goes for men whom she considers to be intellectually superior to her and, since this encourages them to believe it is true, it surely causes certain imbalances in the relationship. As a young adult, Westwood got to London and discovered a bunch of people hamstrung by their own pretensions: they wouldn't go to certain clubs, were afraid of eating on their own, etc. She dived in. "I got this reputation for being a bit of a sex maniac and things like that, and I'm not. I love that Jean Shrimpton quote: 'Sex has never been high on my list of priorities.'"
And while she likes to dress up, she says, she doesn't have to be the centre of attention. Lots of times she just does a thing because "no one else seems to be doing it". Why is it important to dress well? "Just because it is life-enhancing. It's generous. It's a self-expression to find clothes that suit you. And it does make for a communication. We're not naked. I think it's ... yeah." She giggles. "Yuh." She reminds me of a sort of Isadora Duncan figure; one imagines her doing interpretive dance on the lawn of a country house, all diaphanous silk and big gestures, before retiring to the drawing room to talk about socialism.
Westwood already had a child with her first husband, Derek, when she met Malcolm McLaren, and together they set up their shop on King's Road and had another son, Joe. "The recognition of Malcolm ... you see, I came from the north of England and the thing is the milieu into which I was ... culture was nowhere. I was always reading as a child, but apart from that I never went to the theatre; I didn't know there were art galleries. You grew up in this cultural vacuum - well, not quite, I went to a grammar school. Then I met Malcolm and he came from a family of Jewish diamond sellers or something, and he helped me discover things. But now ..." She hesitates. "I don't know what Malcolm's doing, but our interests certainly aren't the same any more."
She brightens. "But my men have always been people who've given me intellectual stimulation. That's what I've always needed. I get that from this husband of mine, who's much younger than me but, my God, he's an original thinker. He's absolutely brilliant."
Her late first husband was apparently unamused by the fame she brought to his name. "My son tells me his father wasn't terribly happy about my purloining the Westwood name. I kept Westwood because when I was teaching I had this little boy, and I kept the name for him. I'd have liked to have changed my name [later], but I was advised by Malcolm that Westwood sounds terribly English, keep it. Anyway, I've got Westwood now."
She and her sons are very close, she says. "I know who they are" - an astute thing for a parent to say of a child. She says: "I always tried to do things by example, even though I was not a very good mother regarding routines and family life. I was not so good like that. And, for example, they weren't allowed to come in and wake me up if they were awake. They were not supposed to come in and jump on you at six o'clock in the morning. Some people let their kids just rule them."
Joe set up the lingerie chain Agent Provocateur and Ben is a porn photographer. "It's true. I mean, he doesn't do very much with it. He's trying to do something with a website at the moment." She falters. "It's very particular. It's got a certain look to it. Mmmm."
To Westwood's delight, her 10-year-old granddaughter is a big reader and has just finished The Catcher In The Rye. "Whenever I ring her, the first thing I say is, 'What are you reading?'"
Westwood once said she'd like Richard Branson for prime minister and Robert Fisk for foreign secretary. One of her protest T-shirts reads I Am Not A Terrorist, Please Don't Arrest Me, and she hates Tony Blair. "I think he's vile. I think he's much more of a monster than Margaret Thatcher. Brown has acquiesced in everything he's done, so I would never vote for a party with Gordon Brown at the head. Never."
A politician she likes is Tony Benn. "Tony Benn was an example of somebody who was a very moral person and very clever, and would've made a good prime minister, probably - I'm not a Marxist, and I shouldn't say that because I don't think he is, either, but that's what he was tarred with."
Did she admire Thatcher? She looks like her, from certain angles.
"The way she dressed was brilliant," she says. "Really, really good. But, no. No. She behaved like a man, really, and I think women could have brought something else." (In general, Westwood thinks it is "better to look important than sexy".)
It is at this point that her husband returns from a frustrating day at jury service. He looks like DH Lawrence, with a big beard and very blue eyes. He is charming to everyone in the room. Westwood gets up and prepares to go downstairs for the photo shoot. "Is that what you're wearing?" says Andreas, frowning suddenly. She nods. "The nail varnish: should I take it off?"
"No," he says. We go downstairs.
"Which shoes?" says Westwood.
"These are less ugly," says Andreas.
"Yes, I see what you mean."
"Hands!" he says, as the photographer starts shooting. "They need to see your waist."
At some point in the shoot, Westwood starts talking about the prisoners at Guantánamo Bay and suddenly gets very animated. "They keep them in these rooms with no stimuli and no light and - they go mad, they turn them to jelly! I think it's absolutely awful." She looks at her husband. "Sorry," she says. "I should concentrate."
Her manifesto, for all the hyperbole, is really just a call for people to watch less television, read more books and buy fewer luxury items. It's not loopy at all. "Of course, they will say, 'What is she doing, she's selling a designer collection, how can she be against consumption?' Well, you have to consume things, of course, you have to live, you have to eat. And I'm not saying don't go to the discotheque, they can do that. I'm just saying go less, do other things." She sighs. "It's so much to tackle."