Livia Firth thinks fast fashion is destroying the industry.The co-founder of Eco-Age, whose husband is the actor Colin Firth, has long championed sustainable fashion and believes high street stores are to blame for the public's obsession with cheap and wasteful clothing. She told the Daily Telegraph newspaper: ''Fast fashion is a phenomenon; you can't make it better. You can use as much organic cotton as you want, but you are still producing one million shorts for their amount of money [too little]. ''It can't be ethical. You are still producing rubbish at the end. Where do all these clothes end up? They have to slow down. They have to change their core business model.'' Livia notably set up the Green Carpet Challenge in 2009, encouraging stars to wear eco-friendly clothing on the red carpet, and uses her status to show that sustainable fashion can be stylish. She also operates by the 30-wear rule, which she says helps her buy quality over quantity. The 44-year-old star explained: ''Eco-Age is all about practical solutions... If you can commit to wearing something 30 times, it's already fantastic, no matter where you bought it. Buy with purpose. ''I have things I wear over and over again. I think I'm one of the few people I know who still mends socks when they have a hole. But it is easier to buy new socks than to mend them, because it's cheap.''