ONE of Katharine Hamnett's oft-used phrases is that we in the UK have become "rotted by comfort".

This was brought home to the designer yet again last weekend when she gave some talks for International Women's Day, and was left thinking that "feminists should stop navel-gazing and show solidarity with their sisters who live in far worse countries under far worse conditions than we do". Feminists, she argues, should be boycotting brands which treat their workers badly. "Write to them [fashion brands]," she says, "telling them you're not going to buy their stuff any more. Don't call yourself a feminist if you're going to buy clothes that are made by your sisters in other parts of the world, who are sitting chained to their sewing machines with ceilings falling from the roofs. You're just a hypocrite."

The 67-year-old designer is, of course, most famous for having hijacked a reception with Margaret Thatcher in 1984, by greeting the then prime minister wearing one of her own-brand T-shirts bearing the slogan "58% DON'T WANT PERSHING" - a reference to polls showing public opposition to the basing of American Pershing missiles in the UK. Rotting in comfort, in other words, isn't her style. Her anger hasn't lessened over the years. The woman who invented the political-statement T-shirt still occasionally wears one, a current favourite currently being: "Leaders Suck." It chimes with her ideas about people power and direct democracy.

Next week, Hamnett comes to Dundee University to talk about fashion and politics in an event linked to Love Your Clothes, a Zero Waste Scotland campaign to encourage fashion-lovers to be more green by choosing clothes that last, repairing them, and buying secondhand. In true Hamnett style, though, her plan is not to focus just on clothes, but on a wider, more political view that encompasses "all the things I care about" - which is really quite a lot of things, from Trident through to pesticide poisoning and the revolutionary potential of direct democracy. "I thought," she says, "I'd come up to Scotland because you guys have already woken up with the referendum."

That said, Hamnett is happy to eulogise about making clothes last. When we talk she's wearing "an old grey wool jumper, an old skirt, which has now got footprints all over it from my dog, and a pair of old tights". She is good at keeping her clothes going. "And I've always done vintage, since I was at college. Before vintage was even invented I managed to snaffle my grandmother's old mink coat and wore it with pride."

Right now, however, she has few of her own-brand clothes to choose from. "I haven't been doing collections for three seasons now and I am running out."

Hamnett regards herself as "quite a green consumer". "Quite" seems something of an underestimate. The fashion designer has long been at the forefront of campaigns against fertilisers and pesticides. Back in the 1980s she campaigned against lead in petrol and recalls uprooting all the wild strawberries growing in her contaminated garden topsoil because she didn't want her children to eat them. Recently, in Hackney, where she lives, she has been campaigning against the use of weedkiller in her local park.

Among the many things Hamnett cares about and which she will mention this Thursday are what she describes as "the nightmares of the clothing industry". The plight of cotton farmers, for instance, who she notes are "dying in astonishing numbers". Many are poisoned by pesticide and more than 270,000 Indian cotton farmers have taken their own lives since 1995. "It's criminal," she says. "On top of that cotton agriculture is poisoning the planet. 10% of world agriculture is cotton, a huge a amount of nitrous oxide emissions given off from the fertilisers, which contributes massively to global warming."

It was 24 years ago that Hamnett first became aware of the impact of the pesticides used in cotton farming and she has been campaigning about it since. "When I first found about it, I thought, 'Gosh people don't know this.' I thought I'd tell them and they'd say, 'That's terrible it must change at once.' But it's been an unbelievable battle and I've felt stonewalled all the way."

The front page of Hamnett's website tells you that the shop is closed. People can't, in other words, go to Hamnett to buy clothes. Rather, you can click through to a fascinating blog, littered with "flashback" posts of past interviews she has done with a range of campaigners from CND's Kate Hudson through to Vivienne Westwood. Hamnett is angry about a lot of things: Trident, the lack of compensation for victims of the Rana Plaza factory collapse in Bangladesh, pollution and so on. The Hamnett we find on her website seems like a Russell Brand of the fashion world - only this activist advocates voting. Indeed, voting is at the heart of her message.

It's fairly clear, speaking to Hamnett, that fashion isn't really where her energies are being directed currently. Rather, it's the General Election - and she has even had a hankering for setting up a new political party. "I was so pissed off," she says, "with the fact our political system is not fit for purpose, that I was going to start a party based on direct democracy in Switzerland, which seemed to me the best functioning model."

Then, she discovered democracy campaigner Richard Wilson's My MP campaign, currently being waged in Stroud, and realised that this might already do the job. Wilson wants all Stroud candidates to sign a kind of Hippocratic oath for politicians. Hamnett believes that if this happened all around the country, then a bloodless revolution would take place. "We would get the nearest thing to direct democracy. We would get real government by the people."

Hamnett has long been adept at "abusing", as she calls it, the opportunities afforded her as a fashion designer to make wider political points. Her anger at the fashion industry remains intense. She rails against brands that "splurge on a fashion show or some stupid event or a dinner for people they want to impress, enough money to feed several families in Bangladesh for many years. It's disgusting and it's got to stop. And if we don't try to stop it we're complicit in it".

Though politics dominate her life and thoughts, she has not lost her love of clothes. That love drives her desire to keep designing "The thing I love about clothes is actually making people look beautiful," she says. "It's a sort of magic trick." Next year, she plans to launch a new shop and a luxury, ethical and environmental line, working with "various co-ops all over the world where they've got beautiful materials - Outer Mongolia, Patagonia".

But isn't there something ungreen in the very idea of fashion? In the rapidly changing styles and seasons, the idea that we need to always be buying some new look? Hamnett believes fashion is an expression of our primal reproductive drive. "It's about sex and status. The girls all want to be the most beautiful girl in the world and if they see someone looking better than they do they want to have something that is as good as that outfit, or better." That has always been there. But, she believes, that drive has been "over-stimulated by the industry. It's been speeded up by the instant media, films, 21st-century technology."

Hamnett seems politically energised but also wearied by all this battling for a more ethical industry. "After 24 years I would have liked to see more change within the industry," she says. "People keep making the right noises, but making noises is all they've been doing for so long."

She wonders if she herself could have had greater impact. "The problem is I tore up all my contacts [after a visit to Mali where she was shocked by the suffering of cotton-farming families]. I tore up my income stream, and in retrospect I think I could have done it a lot more cleverly, phasing out the conventional, phasing in the organic. That way I could have contributed more to sales of organic cotton."

She is hopeful, though. She believes that consumers are now realising that they don't have to buy what's out there. "They're actually expressing this and it's terrifying industry." For Hamnett, simply choosing to buy secondhand is not the sole answer. We should also be making our clothes last. We should be writing to brands and saying we want our clothes to be ethically and environmentally made, and actively seeking out brands which use organic cotton.

"We do need farmers to grow cotton," she says. "They need to earn their living. There's a crisis in West India, where the uptake [of cotton] has been really bad. And they might abandon it altogether or go GM cotton. But we need cotton. It's one of the most wonderful, versatile fibres on earth. It's the nicest to wear. You can do anything with it."

Katharine Hamnett is speaking at Dundee University on Thursday at 12.30pm /