Are discretionary referendums on the EU becoming ‘politically obligatory?’

Do governments call referendums on EU matters because contextual circumstances make them ‘politically obligatory’ or because ruling politicians believe they are the ‘appropriate’ decision-making mechanism? Aude Bicquelet-Lock and Helen Addison argue that, contrary to these suggested reasons, politicians have the freedom to choose whether and when to use referendums strategically to achieve their domestic and European policy objectives.