Great Britain's one million acres of private gardens are under threat as an estimated 20,000 new homes are built every year in back gardens 'grabbed' by developers. Garden grabbing exploits a loophole in the current law which classes private gardens as Brownfield, not Greenfield sites. In this special report, designer Joe Swift sets out to find out just how important our urban back gardens are. And he asks if there are any pioneering alternatives, both here and abroad, to the traditional back garden.