Källor: Johnson stödjer öppna gränser – privat

The United Kingdom's withdrawal from the European Union is commonly known as Brexit, a portmanteau of "British exit". Following a UK referendum held in June 2016, in which 52% of votes were cast in favour of leaving the EU, Prime Minister David Cameron resigned. Theresa May became new Prime Minister and announced that the government intended to invoke Article 50 of the Treaty on European Union, the formal procedure for withdrawing, by the end of March 2017. This, within the treaty terms, would put the UK on a course to leave the EU by the end of March 2019 if no negotiated withdrawal agreement is reached. May has promised a bill to remove the European Communities Act 1972 from the statute book and to incorporate existing EU laws into UK domestic law. The terms of withdrawal have not yet been negotiated; in the meantime, the UK remains a full member of the European Union. The UK joined the European Economic Community (EEC), a predecessor of the EU, in 1973, and confirmed its membership in a 1975 referendum by 67% of the votes. Historical opinion polls 1973-2015 tended to reveal majorities in favour of remaining in the EEC, EC or EU. In the 1970s and 1980s, withdrawal from the EEC was advocated mainly by some Labour Party and trade union figures. From the 1990s, withdrawal from the EU was advocated mainly by some Conservatives and by the newly founded UK Independence Party (UKIP).