Swedish retail giant H&M seems an unlikely poster child for ecological living. The High Street group, which owns brands including Monki and Cos and has more than 4,000 shops across the world, is one of the best known proponents of fast fashion. It’s a cheap and reliable source of trendy clothes which can be discarded as soon as another trend comes in. Yet it has pledged to become “100% circular”, ultimately using only recycled or…