Brexit Explained

Brexit explained in plain English means tracing how the referendum happened, what Article 50 did, and how the UK eventually left the European Union.

This guide explores the background to Brexit, the key events and the agreements that shape UK–EU relations. We distinguish established facts from interpretation, explain important terminology and provide links to primary sources wherever possible.

Our aim is to help you understand the issues, consider different perspectives and draw your own conclusions.

What Is Brexit?

Brexit is the term used to describe the United Kingdom's withdrawal from the European Union (EU). The word combines "Britain" and "exit".

On 23 June 2016, the UK held a referendum in which a majority of those who voted supported leaving the European Union. Following several years of negotiations, the UK formally left the EU on 31 January 2020.

A transition period followed, lasting until 31 December 2020. During this period, most EU rules continued to apply in the UK. On 1 January 2021, the EU–UK Trade and Cooperation Agreement began applying provisionally, establishing arrangements for trade and cooperation alongside the continuing Withdrawal Agreement.

Sources: House of Commons Library — Brexit Timeline | European Commission — EU–UK Trade and Cooperation Agreement

How Did Brexit Come About?

The UK's relationship with European integration began long before the Brexit referendum. On 1 January 1973, Britain joined the European Economic Community (EEC), commonly known as the Common Market.

Membership was debated from the outset. In June 1975, the UK held its first nationwide referendum on whether to remain in the EEC. Of those who voted, 67.2% supported continued membership, while 32.8% voted to leave.

Over the following decades, European cooperation expanded beyond the original Common Market. The Single European Act, which came into force in 1987, laid the groundwork for completing the European single market.

The Maastricht Treaty, which entered into force on 1 November 1993, formally established the European Union. It introduced additional areas of cooperation, including foreign and security policy, justice and home affairs.

Sources: UK Parliament — The EEC and the Single European Act | European Union — History 1990–99

The Road to the 2016 Referendum

During 2015, the UK government negotiated changes to its relationship with the European Union. The discussions covered four principal areas: economic governance, competitiveness, sovereignty, and free movement and social benefits.

On 18–19 February 2016, EU leaders agreed on a new settlement for the United Kingdom. The arrangements were intended to take effect if the UK voted to remain a member of the European Union.

On 20 February 2016, following a Cabinet meeting, David Cameron announced that the government would propose holding the referendum on Thursday 23 June 2016.

The agreement reached with the EU was conditional on continued UK membership. Following the referendum result, the proposed settlement did not take effect.

Sources: House of Commons Library — European Union Referendum Bill 2015–16 | European Council — Negotiations Ahead of the UK's EU Referendum | UK Government — PM Statement, 20 February 2016

The 2016 Referendum Campaign

The referendum campaign brought together political parties, campaign organisations and individuals with differing views on Britain's membership of the European Union.

On 13 April 2016, the Electoral Commission designated two official lead campaign organisations: Vote Leave, which supported leaving the European Union, and Britain Stronger in Europe, which supported remaining. Other organisations also campaigned on both sides of the debate.

The Leave campaign emphasised national sovereignty, control over immigration, the ability to make laws independently of EU institutions and the possibility of developing independent trade arrangements.

The Remain campaign emphasised the economic benefits of EU membership, access to the European single market, international cooperation and the potential economic risks of leaving. Both sides presented competing claims about Britain's future, and the accuracy and implications of particular campaign statements became subjects of public debate.

Sources: Electoral Commission — Designation of the Lead Campaigners | House of Commons Library — EU Reform Negotiations and the Tusk Package

Examining the Campaign Claims

One of Vote Leave's most prominent campaign messages concerned the UK's financial contributions to the European Union. The campaign promoted a figure of £350 million per week and suggested that money could instead be spent on the National Health Service.

On 27 May 2016, the UK Statistics Authority stated that this gross figure did not account for the UK's rebate or payments received from the EU. The Authority concluded that presenting the gross amount as money available to spend elsewhere, without explaining these adjustments, was misleading.

The Remain campaign also used economic projections to support its arguments. In April 2016, HM Treasury published an analysis estimating that, under a particular future trade arrangement, leaving the EU would reduce annual UK economic output by an amount equivalent to £4,300 per household after 15 years, compared with continued membership.

The figure was a modelled estimate of GDP per household, not a prediction that every household would lose £4,300 in disposable income. A House of Commons Treasury Committee report subsequently highlighted the importance of distinguishing these measures and explaining the uncertainties surrounding economic forecasts.

Sources: UK Statistics Authority — Statement on EU Contributions | HM Treasury — Long-term Economic Impact Analysis | House of Commons Treasury Committee — Economic and Financial Costs and Benefits of EU Membership

The Official 2016 Referendum Result

On 23 June 2016, voters across the United Kingdom and Gibraltar participated in the referendum on continued membership of the European Union. The official result was declared on 24 June 2016.

Of the valid votes cast, 17,410,742 (51.9%) supported leaving the European Union, while 16,141,241 (48.1%) supported remaining. Leave received 1,269,501 more votes than Remain.

The referendum attracted a turnout of 72.2%, with 33,577,342 ballot papers counted. There were 25,359 rejected ballot papers.

Source: Electoral Commission — Official Result of the 2016 EU Referendum

The result established a majority for leaving among those who cast valid votes. However, voting patterns differed considerably across the four nations of the United Kingdom.

Sources: House of Commons Library — Analysis of the EU Referendum Results 2016 | Electoral Commission — Report on the 23 June 2016 Referendum

How Did the Four Nations Vote?

Although the overall referendum produced a majority in favour of leaving the European Union, the results differed across the four nations of the United Kingdom.

England voted 53.4% Leave and 46.6% Remain, while Wales voted 52.5% Leave and 47.5% Remain. Scotland recorded a majority for Remain, with 62.0% voting to stay in the EU, as did Northern Ireland, where 55.8% voted Remain.

The referendum result was determined by the total number of votes cast across the United Kingdom and Gibraltar, rather than by separate majorities in each nation.

Voting patterns also varied within England. London was the only English counting region to record a Remain majority. These geographical differences became an important part of subsequent discussions about Brexit and the constitutional relationships within the United Kingdom.

Sources: House of Commons Library — Analysis of the EU Referendum Results 2016 | Electoral Commission — EU Referendum Results by Region

What Happened Immediately After the Referendum?

On 24 June 2016, following the referendum result, Prime Minister David Cameron announced that he would step down. Cameron had campaigned for the United Kingdom to remain in the European Union, but the electorate had voted to leave.

In his statement outside 10 Downing Street, Cameron said that the country required new leadership to negotiate its future relationship with the EU. He indicated that he would remain in office until a successor was appointed and that the decision about when to begin the formal withdrawal process should be taken by the next Prime Minister.

On 13 July 2016, Theresa May succeeded David Cameron as Prime Minister. Her government took responsibility for preparing the United Kingdom's withdrawal from the European Union.

However, the referendum result did not itself end the UK's EU membership. The European Union Referendum Act 2015 did not establish an automatic legal mechanism for withdrawal. Further government action and parliamentary legislation were required before the formal withdrawal process could begin.

Sources: UK Government — David Cameron's Statement, 24 June 2016 | UK Government — Statement from the New Prime Minister, Theresa May | UK Supreme Court — Miller Judgment, 24 January 2017

Article 50 and the Legal Process of Leaving the EU

Article 50 of the Treaty on European Union establishes the procedure by which a member state may withdraw from the EU.

Under Article 50, a country deciding to leave must formally notify the European Council of its intention. This begins a process of negotiations concerning the arrangements for withdrawal and the framework for its future relationship with the Union.

The treaty provides for a two-year period following notification, unless a withdrawal agreement takes effect sooner or an extension is unanimously agreed by the European Council and the withdrawing state.

A legal dispute arose over whether the UK government could trigger Article 50 using its existing executive powers, without first obtaining authorisation from Parliament.

On 24 January 2017, the UK Supreme Court ruled, by a majority of eight to three, that ministers could not use those powers alone to initiate withdrawal. The Court determined that parliamentary legislation was required because leaving the EU would affect rights established under UK law.

The ruling concerned the constitutional authority needed to begin the withdrawal process. It did not determine whether the United Kingdom should leave the European Union.

Following the Supreme Court ruling, Parliament considered legislation authorising the Prime Minister to notify the EU of the UK's intention to withdraw.

The European Union (Notification of Withdrawal) Act 2017 received Royal Assent on 16 March 2017. The Act gave the Prime Minister the legal authority to issue the notification required under Article 50.

On 29 March 2017, Prime Minister Theresa May formally notified the European Council of the UK's intention to leave the European Union. This marked the beginning of the formal withdrawal process, rather than the date on which UK membership ended.

Sources: EUR-Lex — Article 50 of the Treaty on European Union | UK Supreme Court — Miller Judgment, 24 January 2017 | UK Legislation — European Union (Notification of Withdrawal) Act 2017 | European Commission — Notification of Article 50, 29 March 2017

The Brexit Withdrawal Negotiations (2017–2020)

Formal negotiations between the United Kingdom and the European Union began on 19 June 2017.

The initial discussions concentrated on three principal issues: protecting the rights of citizens living across the UK and EU, settling outstanding financial obligations, and addressing the border between Northern Ireland and the Republic of Ireland.

The negotiations also considered how to manage the transition from EU membership to the UK's future relationship with the Union.

In November 2018, negotiators reached agreement on a proposed Withdrawal Agreement, which was endorsed by EU leaders on 25 November.

The agreement addressed citizens' rights, financial arrangements, the transition period and arrangements relating to Ireland and Northern Ireland. An accompanying Political Declaration outlined the intended framework for the future UK–EU relationship.

However, the agreement required ratification before it could take effect. Theresa May's government was unable to secure the necessary support in the House of Commons. MPs rejected the Withdrawal Agreement and Political Declaration in January and March 2019, before rejecting a further motion concerning the Withdrawal Agreement alone on 29 March 2019.

Boris Johnson became Prime Minister in July 2019. His government resumed negotiations with the EU, concentrating particularly on revising the arrangements for Ireland and Northern Ireland.

On 17 October 2019, the UK and EU reached agreement on a revised Withdrawal Agreement and Political Declaration. The principal changes concerned the Protocol on Ireland and Northern Ireland.

Further parliamentary proceedings followed, and the Article 50 period was extended until 31 January 2020 to allow additional time for the withdrawal arrangements to be completed.

Following the December 2019 general election, Parliament passed legislation implementing the revised Withdrawal Agreement. The European Union (Withdrawal Agreement) Act 2020 received Royal Assent on 23 January 2020.

After the remaining ratification procedures were completed, the United Kingdom formally left the European Union at 11 pm GMT on 31 January 2020.

A transition period then began, lasting until 31 December 2020. During this period, most EU rules continued to apply in the UK, although the country was no longer an EU member state and no longer participated in EU decision-making institutions.

Sources: European Council — Withdrawal Agreement Timeline | UK Parliament — Commons Votes on the Withdrawal Agreement | UK Legislation — European Union (Withdrawal Agreement) Act 2020 | European Commission — EU–UK Relations Timeline

The Transition Period and the New UK–EU Relationship

Although the United Kingdom formally left the European Union on 31 January 2020, many aspects of its relationship with the EU remained unchanged during the transition period.

Until 31 December 2020, most EU rules continued to apply in the UK, including those relating to the European single market and customs union. However, the UK no longer participated in the EU's decision-making institutions.

The transition period provided time for the UK and EU to negotiate arrangements governing their future relationship.

On 24 December 2020, the United Kingdom and the European Union announced that they had reached agreement on the terms of their future relationship.

The EU–UK Trade and Cooperation Agreement was signed on 30 December 2020 and began applying provisionally on 1 January 2021. It formally entered into force on 1 May 2021.

The agreement established arrangements covering trade in goods and services, transport, energy, fisheries, social security coordination and cooperation in several other areas.

When the transition period ended, the United Kingdom ceased participating in the European single market and customs union.

Under the Trade and Cooperation Agreement, goods meeting the relevant rules of origin could be traded between the UK and EU without tariffs or quotas.

However, the agreement did not preserve the same trading conditions that had existed during EU membership. Customs declarations, regulatory requirements and other formalities became relevant to trade between Great Britain and the EU.

Separate arrangements for Northern Ireland were established under the Withdrawal Agreement.

The Withdrawal Agreement and the Trade and Cooperation Agreement serve different purposes.

The Withdrawal Agreement established the terms of the UK's departure, including arrangements for citizens' rights, financial obligations and Ireland and Northern Ireland.

The Trade and Cooperation Agreement established much of the framework for the UK's subsequent relationship with the European Union.

Both agreements form part of the legal framework governing UK–EU relations, although additional arrangements and subsequent developments have also shaped how that relationship operates.

Sources: House of Commons Library — End of Brexit Transition: Key Changes and Preparations | European Commission — The EU–UK Trade and Cooperation Agreement | UK Government — Rules of Origin and Claiming Duties | European Commission — The EU–UK Withdrawal Agreement

What Did Brexit Change in Practice?

The end of the transition period on 31 December 2020 brought significant changes to the practical relationship between the United Kingdom and the European Union.

For businesses trading between Great Britain and the EU, new customs procedures, regulatory requirements and rules of origin became relevant. Although the Trade and Cooperation Agreement provided for tariff-free and quota-free trade in qualifying goods, it did not recreate the trading arrangements that existed during EU membership.

The end of EU free movement rights also changed the arrangements for British citizens wishing to live, work or study in EU countries.

From 1 January 2021, British citizens generally became subject to the immigration and residence requirements applicable to non-EU nationals, although specific protections remained for people covered by the Withdrawal Agreement. Special arrangements also continued to apply between the United Kingdom and Ireland under the Common Travel Area.

These changes affected different groups in different ways, depending on their circumstances and the country concerned.

Brexit also required new arrangements for Northern Ireland, where the relationship between the UK internal market and the European single market presented particular challenges.

The original Northern Ireland Protocol was subsequently modified through the Windsor Framework. Other aspects of UK–EU cooperation have also developed since the end of the transition period.

Understanding the consequences of Brexit therefore requires distinguishing the arrangements introduced in 2021 from the changes agreed in subsequent years.

Sources: European Commission — The EU–UK Trade and Cooperation Agreement | House of Commons Library — End of Brexit Transition: Key Changes and Preparations | House of Commons Library — What Does the Withdrawal Agreement Say About Citizens' Rights? | European Commission — The Windsor Framework

Understanding Brexit: Where to Explore Next

Brexit was not a single event but a process involving political decisions, legal changes, international negotiations and new arrangements between the United Kingdom and the European Union.

Understanding that process provides a foundation for examining the practical consequences, the UK's relationship with the EU today, and the questions surrounding its future.

UndoBrexit explores these subjects through evidence, primary sources and clearly identified analysis, helping readers distinguish documented facts from competing interpretations.