--- - |2 Abstract This article examines why the UK Government accepted the 2014 Scottish independence referendum while the Spanish Government opposes a similar referendum in Catalonia. Adopting a most similar research design, we argue that the variation is best explained by perceived political opportunities by the two ruling parties. These are embedded in different conceptions of the state and constitutional designs, mostly mononational in Spain and mostly plurinational in the UK but multiple and contested in both cases. In Spain, vote‐seeking calculations incentivise the Popular Party to oppose a referendum, while its mononational conception of the state and the Spanish constitutional design provide a further constraint and a discursive justification for their position. In the UK, David Cameron's accommodating position was based on the view that the Scottish referendum was low risk – as support for independence was minimal – with a high reward: the annihilation of the independence demand. The Conservatives have recently adopted a more restrictive position because seeming political advantage has changed. The findings suggest that independence referendums will continue to be rare events. - 'Nations and Nationalism, EarlyView. '