The UK’s power supply industry is changing rapidly. Large numbers of new entrants are opening up the market in the supply and production sectors, and at the same time there are moves to increase competition and market-led approaches in what were monopoly sectors, like networks. But this comes at a time when the need to meet long-term public-interest needs – from supporting vulnerable customers to countering climate change – is increasing. This has major implications for expectations of what energy companies, and government, are to deliver and how these outcomes are to be paid for.