Referendums are becoming increasingly prevalent instruments for ratifying constitutional reforms, including sovereignty referendums which determine the critical matter of the territorial contours and national composition of a polity. This paper examines those conditions by studying the responses of mainstream political parties in central office to the sovereignty claims made by nationalist parties in regional office. It takes the view that sovereignty is essentially shared between the regional governments which must make the claim and the central government which must then accommodate the claim and become involved in the referendum’s organization. The paper first asks whether such sovereignty claims exists and contrasts the independence strategies of nationalist parties in Flanders with those in Scotland and Catalonia. Second, it asks what explains the variation in the responses of mainstream parties towards sovereignty referendums, contrasting the cases of Scotland and Catalonia. Third, the paper compares the independence referendums in Scotland with the autonomy referendums held in Lombardy and Veneto in October 2017 to asks how and why mainstream parties are involved in regulating the procedural aspects of the referendum.
