Brexit, a portmanteau of “British exit” was the withdrawal of the United Kingdom (UK) from the European Union (EU) and the European Atomic Energy Community (EAEC or Euratom) at the end of 31 January 2020 CET. To date, the UK is the first and only country formally to leave the EU, after 47 years of membership within the bloc, after having first joined its predecessor, the European Communities (EC), on 1 January 1973. It is also thought to be the first country to withdraw voluntarily from an economic and monetary union of countries (although the UK never adopted the euro). It continued to participate in the European Union Customs Union and European Single Market during a transition period that ended on 31 December 2020 at 23:00 GMT (00:00 CET).

The European Union and its institutions developed gradually, including 47 years of British membership, and grew to be of significant importance to the UK. Throughout that time Eurosceptic groups had existed, opposing aspects of the Union and its predecessors. The public had previously approved the membership of the EC in a 1975 referendum, but no further referendums were held as the project grew and became “ever-closer” in the subsequent Maastricht and Lisbon treaties. Facing pressure from Eurosceptic groups, David Cameron’s pro-Europe government held a referendum in 2016 on whether to leave the EU, which passed by 51.9%. This led to his resignation, replacement by Theresa May, and four years of negotiations with the EU on the terms of departure and future relations. This process was politically challenging within the UK, with one deal rejected by the British parliament, general elections held in 2017 and 2019, and two new Prime Ministers in that time, both Conservative. Under Boris Johnson’s government, the UK left the EU on 31 January 2020 CET; trade deal negotiations continued to within days of the scheduled end of the transition period on 31 December 2020 CET.

Many effects of Brexit depend on how closely the UK will be tied to the EU. The broad consensus among economists is that Brexit will likely harm the UK’s economy and reduce its real per capita income in the long term and that the referendum itself damaged the economy. Brexit is likely to reduce immigration from the European Economic Area (EEA) countries to the UK and poses challenges for British higher education, academic research and security. Following Brexit, EU law and the EU Court of Justice no longer have supremacy over British laws or its Supreme Court. The European Union (Withdrawal) Act 2018 retains relevant EU law as domestic law, which the UK could then amend or repeal.



Following a UK-wide referendum in June 2016, in which 52% voted in favour of leaving the EU and 48% voted to remain a member, Prime Minister David Cameron resigned. On 29 March 2017, the new British Government led by Theresa May formally notified the EU of the country’s intention to withdraw, beginning the Brexit process. The withdrawal was originally scheduled for 29 March 2019. It was delayed by a deadlock in the British Parliament after the June 2017 general election, which resulted in a hung parliament in which the Conservatives lost their majority but remained the largest party. This deadlock led to three extensions of the Article 50 process.

The deadlock was resolved after a subsequent general election was held in December 2019. In that election, Conservatives who campaigned in support of a “revised” withdrawal agreement led by Boris Johnson won an overall majority of 80 seats. After the December 2019 election, the British Parliament finally ratified the withdrawal agreement. The UK left the EU at the end of 31 January 2020 CET (11 p.m. GMT). This began a transition period that ended on 31 December 2020 CET (11 p.m. GMT), during which the UK and EU are negotiating their future relationship. During the transition, the UK remained subject to EU law and remained part of the EU customs union and single market. It was not part of the EU’s political bodies or institutions.

The withdrawal was advocated by hard Eurosceptics and opposed by pro-Europeanists and soft Eurosceptics, with both sides of the argument spanning the political spectrum. The UK joined the European Communities (EC) – principally the European Economic Community (EEC) – in 1973, and its continued membership was endorsed in the 1975 referendum. In the 1970s and 1980s, withdrawal from the EC was advocated mainly by the political left, e.g. in the Labour Party’s 1983 election manifesto.
The 1992 Maastricht Treaty founded the EU, was ratified by the British Parliament in 1993 but was not put to a referendum. The Eurosceptic wing of the Conservative Party led a rebellion over ratification of the treaty and, with the UK Independence Party (UKIP) and the cross-party People’s Pledge campaign then led a collective campaign particularly after the Treaty of Lisbon was also ratified by the European Union (Amendment) Act 2008 without being put to a referendum following a previous promise to hold a referendum on ratifying the abandoned European Constitution was never held eventually pressured the Conservative prime minister David Cameron to hold the June 2016 membership referendum. Cameron, who had campaigned to remain, resigned after the result and was succeeded by Theresa May.

On 29 March 2017, the British government formally began the withdrawal process by invoking Article 50 of the Treaty on European Union with permission from Parliament. May called a snap general election in June 2017, which resulted in a Conservative minority government supported by the Democratic Unionist Party (DUP).
UK–EU withdrawal negotiations began later that month. The UK negotiated to leave the EU customs union and single market. This resulted in the November 2018 withdrawal agreement, but the British parliament voted against ratifying it three times. The Labour Party wanted an agreement to maintain a customs union, while many Conservatives opposed the agreement’s financial settlement, as well as the “Irish backstop” designed to prevent border controls between Northern Ireland and the Republic of Ireland. The Liberal Democrats, Scottish National Party (SNP), and others sought to reverse Brexit through a proposed second referendum.

On 14 March 2019, the British Parliament voted for May to ask the EU to delay Brexit until June, and then later October. Having failed to get her agreement approved, May resigned as Prime Minister in July and was succeeded by Boris Johnson. He sought to replace parts of the agreement and vowed to leave the EU by the new deadline.
On 17 October 2019, the British Government and the EU agreed on a revised withdrawal agreement, with new arrangements for Northern Ireland. Parliament approved the agreement for further scrutiny, but rejected passing it into law before the 31 October deadline, and forced the government (through the “Benn Act”) to ask for a third Brexit delay. An early general election was then held on 12 December. The Conservatives won a large majority in that election, with Johnson declaring that the UK would leave the EU in early 2020. The withdrawal agreement was ratified by the UK on 23 January and by the EU on 30 January; it came into force on 31 January 2020.

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