Forced to accept that intensive farming on the heavy clay of their land at Knepp was economically unsustainable, Isabella Tree and her husband Charlie Burrell made a spectacular leap of faith: they decided to step back and let nature take over. Thanks to the introduction of free-roaming cattle, ponies, pigs and deer - proxies of the large animals that once roamed Britain - the 3,500 acre project has seen extraordinary increases in wildlife numbers and diversity in little over a decade.