For nearly half a century the UK’s Constitution was part of the most globally significant supranational legal order. The UK, like other member states, granted the European Union (EU), or shared with it, competences over entire areas of law making, in order to secure the benefits of harmonisation of rules across the member states. Such deep cooperative commitments within this supranational order are maintained by binding rules, and throughout its membership UK policy makers struggled to reconcile to this loss of freedom of action. After the UK joined the European Economic Area (EEA), a nationwide referendum was held which approved this decision. Over four decades later, amid growing discontent within the Conservative Party over the UK’s EU membership, David Cameron as Prime Minister renegotiated the terms of the UK’s membership and called a referendum on whether the UK should remain part of the EU based on these terms. In June 2016, a majority of referendum voters voted to leave the EU. This chapter explores what the EU is, the consequences of the UK’s membership of the EU for its constitutional order between 1973 and 2020, the process of the withdrawal from the EU and the post-Brexit relationship between these orders.

This chapter examines the system of dispute settlement that is applicable to the Protocol. This system presents a rather unique combination of, on the one hand, the continued jurisdiction of the Court of Justice of the European Union (CJEU) and, on the other hand, an arbitration procedure. As has been rightly observed, these are two very different enforcement mechanisms. The former relies on an existing supranational court which monitors respect for the EU legal order, works together with national courts, and allows some measure of access to individuals. The role of the CJEU is controversial: its case law and jurisdiction were political drivers of the proponents of the withdrawal of the UK from the EU. The latter (arbitration), in contrast, represents a much more traditional public international law method that is new and available only to the parties of the WA.

Taking the long view, the WA is likely to be remembered for two matters: the position it takes on the protection of citizens’ rights (provisions which have the potential, as we shall see, to last for well over a century) and the provisions of the Protocol which could last indefinitely – or perhaps no longer than four years – depending on the outcome of consent votes in the Northern Ireland Assembly. This chapter looks primarily at the effect of the WA in the UK as a whole. It focuses on the implementation of the WA in UK law, the enforcement of rights under the Protocol, as they relate to the UK, and the position on citizens’ rights.

Brexit was a complex political process, no less so legally. It entailed five principal legal instruments. There were two treaties, the Withdrawal Agreement (WA), which settled the terms on which the UK left the EU, and the TCA, which contained the detailed provisions as to the relationship between the UK and the EU on trade and other issues. Then there were three principal UK statutes: the European Union (Withdrawal) Act 2018 (EUWA 2018), which dealt with the acquis of EU law within the UK post-withdrawal; the European Union (Withdrawal Agreement) Act 2020 (EUWAA 2020), which gave legal force in UK law to the WA, in part by amending EUWA 2018; and the European Union (Future Relationship) Act 2020 (EUFRA), which incorporated the TCA into UK law. The focus of this chapter is on private rights that flow from the preceding instruments.

International law is central to the interpretation of both of the Brexit-related treaties. The TCA explicitly requires the parties and any dispute settlement body to interpret it according to the rules of interpretation of public international law, notably the 1969 Vienna Convention on the Law of Treaties (VCLT). The WA, and thus the Protocol, by specifying that any of its provisions concerning Union law or concepts must be interpreted in accordance with EU law (including the case law of the CJEU), implies that its many provisions not concerning EU law will need to be interpreted by the default rules of treaty interpretation, namely those of the VCLT. This chapter provides a brief overview of those rules and some of their implications for these two instruments. It focuses on Articles 31 and 32 of the VCLT, which concern the interpretation of treaties.

This chapter considers how Northern Ireland’s experience during and after Brexit informs our understandings of multi-level governance orders and interactions between and within those orders. A traditional view of governance structures would regard Northern Ireland as having little say in negotiations on trade. Nonetheless, the negotiations on the Withdrawal Agreement have repeatedly seen all parties refer to and return to governance in Northern Ireland as a core concern. This piece will utilise scale theory – originating in political geography – to consider how Northern Ireland became central to the Brexit negotiations.  Scale, as a geographical and political idea, incorporates a range of concepts (core and periphery, population size, majorities and minorities, temporality (linear and nonlinear), geographic governance size), as well as questions of local, national, regional and universal spaces to consider how governance is constructed and the role law plays in constructing scales. Whereas traditional accounts of scaled governance orders deploy “nested” constructs to place Northern Ireland in a tidy frame, organised like a series of Russian dolls, this chapter challenges this narrative by interrogating the slippage between the governance orders and their methods of interaction, and what extent of ‘voice’ that ultimately leaves for Northern Ireland.