The UK has around 29 million homes, and the Energy Performance Certificate database shows that well over half of them carry an energy rating of D or below. Germany, the Netherlands and Denmark have all made faster progress on residential energy efficiency with older housing stock. Britain's problem is not a lack of solutions, it is a collection of specific structural, financial and political obstacles that have conspired for decades to keep cold draughts in and warm air out. Here is what those obstacles actually are, and what works despite them.