What is meant by ‘sovereignty’ and how important was it in influencing the outcome of the Brexit trade negotiations?

The author considers what is meant by ‘sovereignty’ from both an historical and contemporary perspective, taking account of its reference in the context of the Leave campaign in the UK that led to the revised Brexit Withdrawal Agreement with the EU on 17 October 2019, and in the negotiations of the Trade and Cooperation Agreement (TCA) that was signed by both parties on 30 December 2020. The paper explores the classic theory of sovereignty (Herzog, Vettel), with the limitations of its applicability in the contemporary context (Goldsmith, Kreiger, MacCormick, Walker). The paper argues that Brexit was an unprecedented constitutional event where ‘sovereignty’ was a cloak used by the Leave campaign for pursuing a wider range of nationalistic interests and the outcome of the negotiations was closer to constitutional pluralism (Mac Amhlaigh) between the UK and the EU. Although both the UK Prime Minister Boris Johnson and European Commission President Ursula von der Leyen claimed that the TCA was a major victory in the interests of a future trading relationship and respected that the parties are equally sovereign, it does not follow that they are both sovereign equals.