Independence referendums are comparatively rare – and even more so when conducted without the approval of the relevant central government. Referendums on independence in liberal democracies are rare, even more so when held without the agreement of the central government. The constitutional and political response to the Basque precedent had already shaped a legalistic defence against independence referendums in Spain. First, the 2017 referendum was a de facto independence referendum; this kind of referendum generally does not occur in liberal democracies. It draws on their article, ‘The Political Use of de facto Referendums of Independence The Case of Catalonia’, published in Representation.