ROLL UP in a BYD Seal to the leafy entrance of a small housing block in Walthamstow, in east London, and the first thing that strikes you is the quiet. The stylish Chinese saloon is all electric, so you hear no mechanical grind or combustion groan, but so too are the innards of these unusual homes. The hyper-insulated units are powered using solar panels, warmed by electric heat pumps and served by whizzy digital appliances, all tracked remotely with smart electricity meters. Ask a homeowner how the heat pump in his yard works and he says he has no idea and frankly does not care. “Zero bills means zero cost!” he says with a broad smile.