This London Fashion Week, Katharine Hamnett is considering wearing one of her iconic slogan T-shirts, like the ones which lit up the Eighties – Worldwide Nuclear Ban Now, Preserve The Rainforests – which were then adopted by pop bands Wham! (Choose Life) and Frankie Goes To Hollywood (Frankie Say Arm The Unemployed). The big bold lettering on baggy white became a defining look of this politically chaotic decade. This time around, the T-shirt Hamnett is thinking of wearing is simple: Jail Tony.

“We started printing them,” she says, smoking a snout with alarming gusto, “and then I thought, people are going to get arrested wearing this because the laws are getting so tough. And I don’t want people going to jail for wearing a T-shirt. But I might try it out myself. People were fined recently for wearing the T-shirt Bollocks To Blair. That’s very undemocratic. People aren’t taught about democracy at school, people don’t know what it means. My understanding is government by the people for the people and tolerating minority views. Maybe Bollocks To Blair is a minority view. But I doubt it.”

At 59 years old, the woman who invented ‘haute protest’ is protesting ever louder, a life-long agitator who designed the Lebanon-specific Unconditional Ceasefire Now T-shirt for the London protest march last month, and who’s used fashion as a foil for change, for more than 20 years.

“And not to my credit,” she snorts, “because nothing’s happened. Blatantly, marching and T-shirts aren’t enough. If we want change, we’ve got to change the way we go about it. Write to your MP. In your own handwriting. Tell them your views and that you want them represented in parliament. If you ask for a reply, you’re entitled to one by law. If they don’t do anything, tell them you’ll vote for someone who will. All they want is your vote. Power. And why I don’t know; I think politics is a profession more full of personality disorders than the fashion industry. Worse than fashion!”

We’re outside, in the wind, perched on stone-cold steps in a side-alley by her north London studios because she needs “a fag”. A graduate of London’s Saint Martin’s College in 1969, she’s as old-school-up-the-revolution as that year still implies.

“There was a movement to impeach Blair,” she announces, puffing some more, “so I got my other director who’s a Scot, lives in Glasgow, a barrister, to check it out. And he’s using the royal prerogative. So that you can’t impeach him. The Prime Minister can take a unilateral decision and the only person who can stop him is the Queen. It’s time for political reform because we can’t go on like this. I’m ashamed to be British. Blair and Bush have made the world so much more dangerous a place. If nothing changes, it’s just going to get rougher and rougher and nastier and nastier. We’ve got Iraq, Lebanon, they’re pointing at Iran and they’re re-arming Tridents. Bollocks. And nobody wants it! They say desert breaks out in patches, well, we’ve got hell, the day of judgement, breaking out in patches right now. They’re spending our money. Some of my money is on every bullet the British are firing in Iraq. I want my money spent on schools and housing and hospitals and old people’s homes and renewable energy. It’s time for a change! Before we’re killed. I mean, we will be killed…”

Fashion, eh? The flim-flam world of frippery and frocks, unless you’re Katharine Hamnett. We’re back inside what she calls her ‘base camp’, a large, white, open-plan workshop where staff are perched at wooden tables, tape-measures round necks, surrounded by blackboards, paper sketches, rails and rails of her latest collection of toxin-free, ethically sound clothing and an enormous rubber plant which Hamnett is thrilled to observe “has a new leaf!”.

She’s a tall, lean, striking figure with long, jet-black hair, burning brown eyes, wearing no make-up, white plimsolls, a plain white T-shirt and battered jeans, tanned from weeks in Africa (work) and Majorca (holiday), a warm, almost comically intense powerhouse of verbal indignation, the occasional, unexpected, peal of giggly laughter revealing enormous, Joni Mitchell-sized teeth.

In every way she’s less ‘fashion luvvie’ more ‘rock’n’roll nutter’, from the Sixties/Seventies, more Patti Smith than Paul Smith. With a plum-voiced, regal articulacy versed in the well-placed curse. Like a background Bono in the fashion world, she’s a hands-on humanitarian using her position for political change, the first major Western designer to research the impact of the clothing industry on the environment and the people who create the raw materials, the farmers. That was 1989. Seventeen years later, having severed ties with her old toxic licensees in 2004, having survived liquidation in 2001, she’s back in production and her message remains the same, as fully explained in her no-nonsense web-link www.katharinehamnett.com/Protest+Survive/Clean+ Up+Or+Die/Introduction, while her organic cotton collection, Katherine E Hamnett – “E for Ethical, Environmental, or Egomaniac” she grins – goes online this month at www.katharinehamnett.com.

Our throwaway, abundant, mass-market clothes, mostly made from cotton, are currently at their lowest prices since the Thirties depression era due to US, EU and Chinese cotton subsidies, at catastrophic cost to the planet and its people. The statistics on regular cotton farming, which uses enforced pesticides for ‘economic’ gain, are horrendous; deaths via toxic poisoning are now in genocidal numbers (including debt-triggered suicides) while the environment collapses in poisonous chemicals via bleach, lycra, PVC, heavy metals in dyes and leather tanning. The clothing and textile industry employs one billion people, a sixth of the planet’s population, but pay and conditions are diabolical. The industry, meanwhile, says organic cotton farming is too expensive as it adds a feeble 1% to the cost of our T-shirts, a 1%, says Hamnett, “which can make the difference between survival and extinction of 11 million farmers in Africa and a further 90 million in the rest of the developing world”. She spells out her business solution.

“Organic cotton gives the farmers a 50 per cent increase in income,” she says, now perched on a stray stool, sipping some tea. “That makes a huge difference. I was in Mali with Oxfam and it was just horrific – the poverty, destitution – it’s worse than slavery. And when they’ve sold their crop, they’ve got nothing left. If they grow it organically, all the money’s theirs, they have their health and can feed their kids. It’s a long chain, but agricultural companies are getting huge payouts and big business is running government.”

Her dream is to see organic clothing go the way of organic foods, a feasible scenario in a cultural atmosphere where the shape of your “ethical footprint” has never been more fashionable, where giving a shit, full stop, has never been more fashionable.

“Yes, so by definition it might go out of fashion again,” she nods, “but my view is the industry doesn’t care, but people do. Consumers care. You ask any ordinary person. The entire bus queue. All over the world.”

The difference in the clothes, she maintains, is negligible, other than zero complimentary use of “nylon, polyester, metallic finishes, anything too high techy, but you can make proper clothes, gorgeous dresses, soft and silky, in no way brown and lumpy and worthy”. She links the fashion industry back to the war on terror.

“People thought, why do they hate us so much they’d blow us up?” she muses. “And you look at history, colonialism, the terrifying things we did. Nobody is going to hate you that much without having some reason to hate you. And you think, how can we make up for that? Part of it is demanding proper deals for developing world farmers. The Brits went into the textile industry in the 18th century and wanted the Indian market. They found the Indian spinners could spin finer yarns than spinners in Lancashire. So they went in and cut off their fingers. You know? Great! We’ve stolen all their minerals. We’re cheating them out of their crops. And it’s time we did something about it.”

Hamnett’s busy, chaotic office is not littered with Vogue magazines, but The Ecologist, The Economist, a colossal map of the world and torn sheets from The Herald Tribune on the water wars in the beleaguered Turkish region. Listening to her is like taking The Armageddon Tour of Earth, via the crimes of politicians and big business, via her unshakeable belief in Consumer Power. We can, she insists, make or break big business: just take our money away. She’s a boycott believer, calling for the boycott of every toxic, corrupt, inhumane corporation we know about (and investigations of the ones we don’t), even if that means, maybe especially if that means “boycotting our favourite brands. And writing to them and telling them why. Industry is more powerful than government. And industry listens”.

On the even larger scale, she’s calling for “political reform”, citing Swiss Democracy as a template, the lone country which has referendums on everything, where 50,000 public signatures on a petition (gathered within 100 days) guarantees a national referendum “on all the big issues. On nuclear power recently, the government was defeated. They’ve accepted they’re not having it. We don’t need leaders. The Greeks didn’t have leaders. Our two-party democratic system is not working. Politics is over. Kick ’em all out is my view!”

Still, we’ve always got the caring, sharing Conservatives ready for the rescue. “They can all go to hell,” she roars. “They’re all as rotten as each other. Cameron looks cute. Blair looked cute, remember? And d’you think Brown is going to be any better because he’s a Scot? He’s a city puppet. He was giving a speech to the Lehman Brothers who are heavily involved in Enron, saying what an honour it was to have them in the country and they’re involved in dreadful shit. F**k off!”

Where Bono has long credited ‘the spirit of 1976’ and ‘Catholic guilt’ for his life-long drive to stop the global madness, Hamnett credits her family’s contributions to the second world war. She lost two uncles in the Air Force while her father, also in the RAF, was a prisoner of war in Burma for three years.

“I just feel, while there’s breath left in me, it’s unfinished business,” she says. “My uncles, like millions of people, gave their lives, that the world would be free of fascism. And it’s not over.”

Born in 1947, her father’s career meant she lived in France, Sweden, Romania and England and remembers a pivotal political moment aged four, echoing today’s blanket fear of the men in beards.

“My father was quite dark,” she chortles, “and I remember coming back to the UK from camping in the south of France and they wouldn’t let us in. Too brown. Thought we were immigrants! He was in the RAF and they wouldn’t let us in. Of course, now, if you’ve got a sun-tan and a rucksack, don’t run, is the message.”

After 10 schools, including the primly English institution of Cheltenham Ladies College, after her BA in Fashion And Textiles at St Martin's, she went on to invent, alongside the protest T-shirts, distressed denim, stonewashing, stretch denim and power dressing’, becoming British Designer Of The Year in 1983, which she celebrated in 1984 with her spirited encounter with Margaret Thatcher, wearing the T-shirt which read 58% Don’t Want Pershing, a protest over the Pershing nuclear weapons Maggie and chum Ronnie Reagan were deploying throughout Europe.

“I had a coat on and knew I had about 15 seconds to get that picture,” she smiles. “I went in and she said, ‘Oh, at last a true original’ because I was dressed in tatty white and everyone else was in dreadful ball gowns. She was very charming. I opened the coat and she said, ‘Ew, you seem to be wearing a strong message’ and then this proper noise came out, ‘Ewwwwuuurck!’, a squawk, like a chicken!”

The Eighties catwalk belonged to Hamnett, as famous and recognisable as any of the plume-haired pop folk of the day. “I’ve been really lucky,” she decides, “I’ve checked out fame and success. And fame was really irritating. I’ve got friends, actors, who can’t go anywhere because they get mobbed and it’s horrible, it’s not funny. I like to be invisible. I used to wear dark glasses through the Eighties so when I took them off nobody ever recognised me. And it worked. With success, you’re just glad it’s working, because everyone said you were mad. That was quite gratifying. And, hell, it was fun. It was an incredible privilege, I met Nelson Mandela, amazing people, I’ve been to gardens in Japan you needed government permission to get into. Makes a change from climbing over the bloody walls!”

Today, she has two sons (30 and 25) and credits them, too, with her uncompromising world-view, “mother to one, mother to all really”, while a third, more esoteric reason for caring this much emerges.

“Why are we here?” she ponders. “What are we supposed to be doing? Where it says in Genesis ‘Man was given dominion over the Earth’, the original Greek translation is ‘custodianship, partnership, guardianship’ and isn’t that a good reason to be here? Life is amazing. You’ll know that in Scotland, you see the beauty, the chain of symbiotic relationships, how everything is designed so perfectly to survive. We should be fostering the planet, making sure not even one species dies.”

You hippy.

“I don’t think that’s hippy,” she balks, “I was never a hippy! I couldn’t afford to be a hippy. And I’d be bored shitless in five minutes. I’m rational and a realist. All that new age bollocks as well, it can all go to hell. Even star signs. If I was ever out on a date, honestly, if they asked me what my star sign was, I’d get up and leave. I wouldn’t even finish my drink. Uh! Can’t stand it. I’m a pragmatist; I’ve been running my own business since I was 21.”

You wonder, since her graduation year zero, ’69, if she really thinks there’s been no humanitarian progress. In almost 40 years?

“There hasn’t been progress,” she insists. “People are poorer than they were 40 years ago in poor countries. Here we are in convenience and comfort and we’re no happier. Bad companies have got bigger. We’ve got fewer freedoms than we had before. A good thing is the internet, where people can talk freely and blogs are scaring politicians. And young people really care.”

A suggestion is made, unhelpfully, that perhaps mankind is fundamentally useless, that we’re skewed by the selfish gene, that people won’t write to their MPs, or boycott companies, cocooned in their comforts, possessed by self, obsessed by surface, paralysed by the idle cynicism which says all this mess is just the way things are and the way they’ve always been.

“Well, look at all the civilisations and cultures which lived in harmony with nature,” she counters. “What we’re talking about here is greed and Western civilisation aren’t we? Everybody I talk to, within 30 seconds they’re talking about important things, about Blair backing America especially and they’re so angry. People do care. They just don’t know what to do. These are things they can do.”

For the last three years, while sourcing her E collection on “no income” she’s been working with Oxfam (among others) on ethical technology, in the new emissions-cutting realm of concentrated solar power “which can desalinate sea water, create fresh water and create electricity at the same time just by using sunshine. They’re finding ways to provide the entire planet’s electricity needs with this. It’s a miracle! Which no one ever mentions”.

She’s lived on the same street as the old Arsenal football ground for 30 years and her interest in popular entertainment culture is, unsurprisingly, nil: “Oh, it’s all just becoming more superficial and more materialistic, the people who are famous for being famous, well it’s just beyond stupid, isn’t it? Run like hell!”

Hamnett has no problem with being one year shy of 60: “It’s quite nice, becoming older. Age is a licence. So watch out. What doesn’t kill you makes you stronger is true; everyone has their fair share of sorrow and you become more confident. You know what matters and your priorities are straight. You’re kinder. Mind you, I was just reading about how you should learn to forgive people their shortcomings. What!? I’ve never tried that.” Her E collection, meanwhile, could pioneer an actual revolution in global cotton farming.

“Remember aerosols in the Eighties?” she beams. “We were told aerosols were blowing holes in the ozone and the companies said (airily) ‘Oh yes, yes, we’ll phase them out in two years’ and they had to replace them immediately because sales dropped dead. That’s the kind of consumer action we’re looking for. We’re doing a T-shirt, ‘I Shop Therefore I Rule’ and it’s true, it’s about consumer power. And how we consume decides the future of the planet. And it’s practical. We give 15 per cent to a charity which helps the farmers and the other great thing is it’s tax deductible. We’re making profits which we don’t pay tax on and at the same time protecting and developing our supply chain. So even if you’re an arch c***, it makes economic sense.”

She roars with laughter and contemplates those arch enemies.

“What do the rich want another 20 million for?” she wonders. “I’ve got a friend, she’s a gardener who does million quid gardens. And I say ‘Well, have they got any taste?’ and she says, ‘No, never.’ Go down Bishops Avenue (London’s Millionaire’s Row, currently home to the UK’s most expensive home, at £50 million) – some of the ugliest houses you’ve ever seen in your bloody life. Shit holes! It’s personality disorders, lack of love in childhood, they don’t know what love is or how to share it. It’s just more, more, more, mine, mine, mine. Sad! You go on the beach, everyone takes their clothes off and there are all the rich fat ones. Physically hideous. Unloved. And wrong. Wrong!”

She escorts me to the doorway and tells me one last time.

“We need political reform,” she stresses, “because we’ve had enough of this shit. In who’s interest is all this? Not ours. You have your vote and you have your wallet. I think this is the moment. I think this is our last chance. Now!”

She scribbles on her hand, an imaginary note.

“You will write letters, won’t you?” she says, those intense brown eyes still burning with hope. “Won’t you?”

For more info go to www.katharinehamnett.com