The populist challenge to multilateral diplomacy: Brexit and the demise of UK-EU security cooperation

How do the actions of politicians come to intrude on cooperative diplomatic practices? The rise of populist movements the world over has made this an important question, given the challenge they pose to the administrative state. While Practice Theory (PT) in IR and diplomacy studies theorises ‘the political’ into everyday diplomatic activity, its emphasis on competent performance within diplomacy – and diplomatic continuity – understates the challenge from populist politics. This article charts the emergence of a specific form of populist practice – with its own standards of competence – that has come to shape partisan politics and to constrain and delimit diplomatic practice. Our argument is illustrated through a study of post-Brexit UK-EU security cooperation. Drawing on elite interviews, we show how Boris Johnson portrayed his predecessor’s efforts to maintain continuity in the security relationship as incompetent politics, subsequently upending the diplomatic relationship to successfully achieve political mobilisation.