With the lowest levels of energy efficiency in Europe, the UK's domestic building stock is a huge opportunity for market growth. Successful delivery of a sealtight, nationwide, retrofit programme underpinned by pioneering UK technology, a move away from gas and sufficient government support, could bring societal-wide benefits, reducing fuel poverty, improving energy security, reducing a major source of UK emissions and a tenfold growth in this economic sector. The question is of delivery. How do we do it? How do we retrofit the 19 million homes in desperate need of pioneering heat pump and energy efficiency technologies? Which policies, targets and government incentives will aggregate demand and accelerate market take up? Crucially, is the supply side ready?