Given that Britain is a nation of shopkeepers, so it should come as no surprise to find yet another glamorous shop opening in the chichi streets of West London. What does come as a surprise is who owns it – the actor whom Rupert Everett rather miserably called a “ghastly guitar-playing redbrick socialist” and the heart-throb whose wet clothes made him more desirable to womankind than if he’d stripped them off entirely. Yes, Colin Firth.

Although the actor is, as he happily admits, “an unlikely shopkeeper” (and is now on friendlier terms with Everett, having worked with him on two films, The Importance of Being Earnest and next month’s St Trinian’s), his plant-covered, four-storey emporium on Chiswick High Road will be his third foray into retail. His first two were the ethical-coffee cafés Progreso, in Notting Hill and Covent Garden, set up to benefit Fairtrade growers. This latest venture will be run on the same socially responsible theme.

Called Eco, the shop will be Britain’s first “ecological destination store”, offering not just contemporary, artisan-made, ethical, Fairtrade and eco goods, but the services of environmental experts to help homeowners make their spaces more energy efficient.

To be fair, the shop isn’t only Firth’s. He is what he calls “a handy communications device”, and one of four shop owners, the other three being his wife, the beautiful and spirited Italian documentary producer Livia Giuggioli, her 26-year-old brother Nicola, and friend and investor Ivo Coulson. But he is, as Livia says, “an essential part of the project. Colin’s one of those people who researches everything properly. He’ll get obsessed with something like the Iraq war and then wake up in the middle of the night wanting to talk about it.” (Or, as she puts it later, with characteristic passion, while the Englishman grimaces at her forthrightness: “We’re a great match because I’m the ballbreaker and he’s the brains.”)

While the even-more-gorgeous-in-real-life Mr Firth will clearly play a major role in luring customers into the shop, there is no doubt that it is the eco-aware Giuggiolis who are the project’s directors. As children, growing up in the Italian countryside, Nicola says, “We lived a very eco life, although we didn’t know that’s what it was. Even 15 years ago, our parents used energy-saving bulbs that took half an hour to emit light. We ate local, organic food. Nothing was thrown away. But that’s just how it was in Italy. And I liked learning about it: after university, I decided to do a PhD on alternative energy sources to oil. So, this is a natural progression.”

Sitting in the Firths’ book and art-filled West London sitting room (where Livia proudly shows off a cushion she’s made from a pair of old Armani trousers, and her husband is admiring a wireless device that digitally displays how much electricity their home is using), it soon becomes clear that this shop isn’t just a commercial venture. And it’s not a flight of luvvie fancy, either.

They’ve investigated the market, seen that there’s no central retailer-cum-consultancy to which people can go for ecological building and decorating advice and filled the gap, says Ivo Coulson. And they’ve devised the shop experience so that it’s fun: as well as the eco-products on sale, there will be events and exhibitions of ethical art, curated by hip London designers Marcus Fairs and Barley Massey. “We want this to be a good place to meet, and enjoy, as well as learn how to improve the planet,” says Nicola. “And to do that it has to be fashionable, to have things for all generations. It can’t be an eco-nutter place or it won’t work.”

The building itself, they hope, will become not only Britain’s first self-sustainable shop, lit by the sun, clad in plants and solar-heated, but a place where people can come and touch, feel and learn. On the roof, there will be solar panels to examine (“You can get see-through ones now, shingle, brick, all sorts,” Nicola says), wind turbines to watch, green-roof insulation systems and garden solar lighting to see (Colin’s favourite product being a jam jar containing a solar-powered bulb).

Inside are all sorts of odd things to fill consumers’ new eco-designed spaces. In one corner sits a simulated office filled with sustainable products, such as a bamboo computer, recycled pencils and a solar mobile-phone and MP3 charger. There’s a section offering energy-saving kitchen appliances. Another offers DIY stuff like natural paint and paper. And, on the ground floor, there’s a range of gifts and gadgets: Estonian Christmas decorations for £1.50, eco-friendly Nest cleaning products, hangers recycled from old chairs, £3,000 Hans Wegner chairs crafted from sustainable wood. In the basement will be the consultancy, stocked with samples of eco-flooring, cladding, tiles, radiators and pipes, so, “Rather than spending hours on the net trying to track down a sustainable product from abroad, you can take a look at it here and discuss how to build with it,” Nicola explains.

While the young Italian is clearly pretty authoritative on all things green, his English brother-in-law admits, slightly shamefacedly, “I’m no eco hero. I’m supporting the shop because I think it’s a good idea. If I’m in a position to say anything, it is because I’m one of the culprits. I’m culpable because I’m a consumer. When you start to think about global warming, Western over-consumption, our energy wastage, it makes you want to improve the negative effects of your complicity in it.”

Neither of the Firths is averse to adding their voice to a campaign, if the cause is one they believe in. As a child, Colin door-knocked with his father for the Liberal Party, handing out pamphlets. The couple have both been vocal about the needs of Congolese refugees in the UK, Colin taking part in public demonstrations, and have been to Ethiopia with Oxfam to highlight the plight of coffee farmers “whose weekly wage is what you would pay for a single coffee”, he mutters. And, at the British Film Festival, Livia’s first project as executive producer, working with Amnesty International, is about a man who’s been on death row, after a flawed trial, for 25 years.

“The thing is, if you have been given the privileges we have,” says Firth (between bursts of chat about the failure of the Doha trade talks and real change after the G8 summit, trying to meet Peter Mandelson to protest against unfair European bilateral trade agreements, the effect of dumping subsidised American rice on Haiti, and what he calls “the great rip-off of British coffee drinkers at the expense of Ethiopian farmers”), “if you have this many perks, surely you can help out. Rather than being a luvvie with a lofty opinion preaching to people, I prefer to do things, to get involved, put my money where my mouth is and learn along the way.”

So, will he help out behind the till? “God, no!” he groans, covering his eyes in horror, as his wife threatens him, laughingly, with Wednesday-afternoon shifts. “I worked in the café when it opened and the coffees I made were probably the worst we ever served.”

No chance, then, of him putting in a guest appearance in what many women might hope would be the Eco uniform: a wet white shirt? “Perhaps if it’s eco cotton and recyclable water,” he grins good-naturedly. “Depends how badly we need the customers. At the moment, I’ve got three films out and all anyone wants to talk about is the shop. So, hopefully, another drenching won’t be necessary.”

Eco opens on December 1, at 213 Chiswick High Road, London W4 (www.eco-age.com )

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