As the founder of ethical clothing label Edun, Ali Hewson – also known as Mrs Bono – is on a mission to give something back, she tells Carola Long

For someone who runs her own fashion label, throws herself into promoting charitable causes, is married to the world's most prominent rock-star-turned-campaigner and has four children, Ali Hewson is very calm.

Bono once said that there was, "something so still about her," and apart from visible coyness about being photographed – she asks nervously if she looks ok because she hasn't seen a mirror – it's true. It must be this composure that has enabled her to stay grounded whilst globetrotting, multi-tasking and generally throwing the metaphorical juggling balls higher than most. Although the very pretty 48-year-old founder of the ethical fashion label Edun clearly feels strongly about her latest charity T-shirt project, and the need for more thoughtful consumerism, there's no guilt-inducing alarmism or tub-thumping in her manner. Rather, Hewson's calm explanation of her philosophy, and of some of the horror and suffering she hopes to alleviate through her business, is all the more persuasive for being so serenely delivered.

When we meet in the plush personal shopping suite at Selfridges, before the launch party of Edun's new charity T-shirt collaboration with the magazine Dazed and Confused, she solicitously offers me a glass of water, then explains why she wanted to support the children's charity Warchild by donating 15 per cent of the proceeds from sales of the limited edition T-shirts to its projects in the Democratic Republic of Congo.

Hewson says: "I came across Warchild's work when I was in Kosovo, and I wanted to support them because they are working in the Congo and there are so many problems there." Although the country held its first free elections in four decades in July 2006, its people still face violence, rape, looting and displacement. In her soft, sympathetic Dublin tones, the kind that make you donate money to a cause before you even know what it is, she adds that "children are always the silent innocent victims of war and Warchild are just trying to stem the bleed."

She is sweetly excited about the T-shirts – she's wearing one with Chanel wedges, a black blazer and skinny black jeans – and her smokily made-up eyes brighten as she explains how nice and long they are, and how the fact that animal motifs are having a bit of a moment, (apes at Christopher Kane, wolves everywhere) was a happy coincidence, as all she had in mind for their illustrator Jo Ratcliffe was something "raw and Africa-focused".

Hewson's interest in Africa began when she was 24, and she and Bono worked in refugee camps in Ethiopia for five weeks after Live Aid. She says she was "prepared for what it would be like when we were there, even though it was really tough, with terrible hunger and starvation and people dying every day. It was when I came back that I found it strange going into a supermarket, because I was overwhelmed by the fact that you could actually buy food."

She has seen since been all over the continent ("because of the type of images we see of Africa, I don't think people understand how vibrant and sexy and beautiful it is. There is something amazing about the people, something very spiritual," she says) and most of Edun's clothes and accessories are made in sub-Saharan Africa.

The label's mission is to create sustainable employment in developing economies and to act as a voice encouraging the fashion industry to trade with Africa. Its focus is ethical rather than eco, but Hewson is working towards using more organic cottons in her collections.

After meeting Bono, Hewson focused on bringing up their two girls and two boys, and the couple had a rule that they shouldn't spend more than three weeks apart. However, in 2005 she and her husband set up Edun because "Bono and I wanted to trade on the ground with the government, to put our money where our mouth is, and find out how easy or difficulty it was." She says: "It was a huge learning curve as I have no experience at all. It's just basic common sense, and the rest is obstacles."

Hewson's only fashion training, of sorts, was the charity fashion shows she organised in Ireland in the late Nineties, for which she brought over "Naomi, Christy and Helena" (Naomi Campbell used to date U2's Adam Clayton). She says she's not even a big shopper – although her habit has grown – and she wears her clothes "to death" because "it's me. I don't mind clothes with holes." Despite this lack of concern about toting the latest 'it bag', Hewson isn't entirely unconcerned about protecting her image. When I ask if she's made any major fashion mistakes over the years, she gasps, half joking, half alarmed: "Are you going to pull up the photograph and stick it on the page? I've made sooooo many. Everything was a fashion mistake. When Bono and I met at school [Mount Temple Comprehensive in north Dublin] I was wearing Wellington boots, jeans and those Shetland jumpers most days. We went to a school that had no uniform and it was an anti-fashion statement," she says.

"We couldn't afford high fashion and we didn't want to follow anybody else's trend."

Has Bono, whom she married at just 21, ever made any fashion mistakes? (It's a rhetorical question, surely. There's that mullet for a start.) "Erm..." Have you ever confiscated anything out of his wardrobe? "Yes, but I'm not telling on him. I hope I haven't influenced his dress sense, although if I say I like the blue trousers he will put on the black ones, so it's always a struggle."

As well as sparing her husband's sartorial blushes, Hewson is also keen to protect the image of her projects when she deems it necessary. Behind the gentle exterior and youthful prettiness, she is determined. Nude, the natural skincare company she started with Fresh & Wild founder Bryan Meehan, considered Stella McCartney's perfume Stella Nude to be an infringement of their trademark and took the case to court. In August the High Court ruled that Nude skincare had a clearly arguable claim of trademark infringement. A trial is set for the new year, and it has been made clear the topic is off-limits for now. While she might be clashing with one brand, Hewson has happily merged with another: LVMH. The French luxury goods conglomerate bought a 49 per cent stake in her Edun label last May. Hewson explains that she made the decision because, "being a tiny company, you get to a place where you really need to move up a gear". Arnault's decision to invest reflects not only Hewson's clout and contacts book but also an overdue increase in the fashion industry's and consumers' awareness of ethical issues.

She says, "I think that there hasn't been enough attention paid in the industry to what happens, say, when a label moves from one company to the next to save 20p. It has become a big machine and it has made mistakes because of that. The consumer is now thinking, 'What are my clothes about?' and if something doesn't have a good story and it's not transparent, people won't want it."

In her gentle, rather than evangelical manner, Hewson acknowledges that, "most of the time I want to know where something came from, but it's very hard to shop that way.

"It's an interesting time, and a new process, and it's the desire of the manufacturers to change that is the important thing." If other labels can match the strength of Hewson's thirst for change, fashion's collective conscience could become a lot clearer.

The Edun T-shirts are available at the pop-up shop in Selfridges and at