Political discontent remains a pressing issue for UK parliamentary democracy that needs to be better understood. We offer a range of theoretical perspectives on dimensions of political disaffection and seek to measure them with substantially new survey measures that assess how citizens perceive the performance and motivation of politicians. Our results indicate that the public's critique of politics and politicians takes a number of different forms, which varies in predictable ways across social groups and according to other political and attitudinal measures. Mainstream parties are ensnared by political discontent, but other parties can be beneficiaries of it. We show that discontent is at least as important a driver of UKIP's support as social, cultural, demographic or economic factors.