Brexit is the term used for the United Kingdom's withdrawal from the European Union. The word is a contraction of British and exit and became widely used during the political debate surrounding the UK's membership and withdrawal. In the 23 June 2016 referendum, a majority of participating voters voted to leave the EU, after which the UK government initiated the legal process for withdrawal under Article 50 of the Treaty on European Union.
The UK formally left the EU on 31 January 2020. Brexit therefore describes a constitutional and international process rather than a single event. It involved negotiations over the terms of withdrawal, a transition period, the future UK EU relationship and subsequent changes to domestic law, trade arrangements, immigration rules and regulatory relationships. The term can refer broadly to the political process, the withdrawal itself or the period of institutional change associated with leaving the EU.
The formal withdrawal was governed principally by the EU UK Withdrawal Agreement. The UK ceased to be an EU member on 31 January 2020, but a transition period continued until 11pm on 31 December 2020. During that period the UK was no longer an EU member but remained subject to EU law under the Withdrawal Agreement and remained in the EU single market and customs union for the transition period.
This distinction is important because Brexit did not produce an immediate change to every practical relationship at midnight on exit day. The transition period provided time for businesses, public authorities and individuals to prepare for the new relationship. At the end of the transition period, the UK was no longer part of the EU single market or customs union and EU law ceased to apply to the UK as EU law, subject to the specific arrangements established by the Withdrawal Agreement and subsequent domestic legislation.
The Withdrawal Agreement dealt with matters arising from separation, including citizens' rights, financial obligations and arrangements concerning Northern Ireland. It also created a transition period and institutional mechanisms for resolving issues arising under the agreement. A separate Trade and Cooperation Agreement was signed between the UK and EU on 30 December 2020 and established much of the framework for the post transition relationship.
The Trade and Cooperation Agreement covers areas including trade in goods and services, fisheries, law enforcement and judicial cooperation, transport and social security coordination, although it does not reproduce the level of economic integration that existed during UK membership. Brexit therefore involved two related but legally distinct stages, first the settlement of the withdrawal and second the establishment of the future relationship.
One of the most significant consequences of Brexit was the change in the UK's relationship with the EU single market and customs union. EU membership had involved participation in the single market, whose four freedoms concern goods, services, capital and people. After the transition period, the UK and EU became separate regulatory and customs territories, although the Trade and Cooperation Agreement established preferential arrangements for substantial parts of bilateral trade.
Businesses trading across the new border can face customs declarations, rules of origin requirements, regulatory requirements and other procedures that did not generally apply to UK EU trade while the UK was a member of the EU customs union and single market. The exact requirements vary by product, destination, regulatory regime and the applicable agreement. Brexit therefore changed the legal architecture governing cross border commerce rather than simply ending political membership.
Brexit also changed free movement arrangements. While the UK was an EU member, EU free movement rules provided a legal framework for qualifying EU citizens to live and work in the UK and for qualifying UK citizens to live and work elsewhere in the EU. Following the transition period, the UK implemented a new immigration framework and free movement between the UK and EU ceased to operate as it had during membership.
The Withdrawal Agreement preserved specific rights for people covered by its provisions, including many EU citizens already living in the UK and UK citizens already living in EU member states before the relevant deadlines. Brexit therefore distinguished between rights arising from previous residence and the new immigration rules applying to future movement.
Brexit also affected the UK's domestic legal framework. The European Union Withdrawal Act 2018, as amended, provided mechanisms for converting much directly applicable EU law into domestic law at the end of the transition period, creating a body of domestic legislation that was initially described as retained EU law. This was intended to provide legal continuity while allowing subsequent governments to amend or repeal inherited rules. Brexit therefore involved both an international constitutional change and a substantial domestic legislative programme. Parliament, UK courts, government departments, devolved administrations, regulators and businesses all had roles in adapting to the new legal environment. The process also interacted with constitutional questions concerning the distribution of powers between Westminster and the devolved governments.
The political significance of Brexit arose partly from competing views about sovereignty, economic integration, immigration, regulation, democratic accountability and the UK's international position. Supporters of leaving commonly emphasised national decision making and control over policy, while supporters of continued membership emphasised economic integration, mobility and collective influence. These were political arguments rather than technical definitions of Brexit itself. The referendum result established the political mandate for withdrawal, but the precise form of Brexit remained subject to subsequent negotiations and legislation. The resulting settlement therefore cannot be understood solely from the referendum question. It depended on the Withdrawal Agreement, domestic legislation, the Trade and Cooperation Agreement, subsequent negotiations and the practical implementation of new border and regulatory arrangements.
Brexit is best understood as a multi year process of constitutional, legal, economic and institutional separation between the United Kingdom and the European Union. The UK formally left the EU on 31 January 2020 and completed the transition at 11pm on 31 December 2020. The consequences extend beyond trade because EU membership had affected immigration, law, regulation, security cooperation, agriculture, fisheries, research, regional funding and numerous other areas.
Brexit did not mean that the UK ceased all cooperation with European states, because the UK and EU remain linked by treaties and continue to cooperate in many fields. The fundamental change was that the UK ceased to be an EU member and therefore no longer participates in the EU's institutional and legal system as a member state.
