This article asks whether populism poses a problem for the UK Constitution. It explains how it is easy to be complacent about the extent to which populism may undermine the UK constitution. Populism may merely be a short-term corrective to tensions inherent to liberal democracies. Moreover, the UK’s characterisation as a predominantly political, evolutionary constitution may make it easier for populist movements to correct flaws without populist movements collapsing into authoritarianism. The article argues, however, that this complacency is misplaced. It fails to take account of the threats populism may pose to democracy, particularly through the homogenisation of the will of the people and the undermining of deliberative and participatory democracy through the over-simplification of politics combined with a focus on emotions over rationality in political debate. Rather than being immune to the dangers of populism, the UK constitution may act as a catalyst for populist movements, particularly given the way in which it focuses on pragmatic as opposed to redemptive understandings of democracy and human rights. Moreover, its flexible, uncodified nature may mean that the UK constitution is less able to prevent populist movements become authoritarian. Having established these difficulties, it then suggests a series of possible reforms. More fundamentally, it argues that it is time to revisit why we regard parliamentary sovereignty as the key principle of the UK constitution, arguing that we need to see this principle as instrumental to maintaining a balanced constitution, as opposed to upholding the sovereignty of the institution of Parliament.