UK Politics and Brexit: Origins to Today

**The Bloomberg speech.** The modern UK–EU file begins, by most accounts, with David Cameron's speech at Bloomberg's London headquarters on 23 January 2013. Facing pressure from the UK Independence Party and from Conservative Eurosceptics, Cameron committed to renegotiating the UK's terms of EU membership and putting the result to an in/out referendum after the next general election. Cameron won the 2015 election with a majority — partly on the strength of the referendum pledge — and the referendum was held on 23 June 2016.

**The referendum.** The Leave campaign won with 51.9 % of the vote on a 72.2 % turnout — the largest democratic vote in UK history at the time. The result split deeply along geographic, generational, and educational lines: London, Scotland, and Northern Ireland voted Remain; most of England and Wales voted Leave. Cameron resigned the morning after the result and was succeeded as Conservative leader and Prime Minister by Home Secretary Theresa May in July 2016.

**The Article 50 period.** Article 50 of the Treaty on European Union was triggered on 29 March 2017, starting the formal two-year clock to withdrawal. The May government called a snap election in June 2017 hoping to strengthen its negotiating position; instead it lost its majority and governed thereafter with parliamentary support from the Democratic Unionist Party of Northern Ireland — a political dependence that would shape the Northern Ireland file decisively.

The May–EU negotiation produced a Withdrawal Agreement that included an Irish border "backstop" designed to prevent the return of a hard border on the island of Ireland. The backstop was repeatedly rejected by the House of Commons in early 2019; May resigned in May 2019.

**The Johnson government and exit.** Boris Johnson took over as Conservative leader and Prime Minister in July 2019. He renegotiated the backstop into a Northern Ireland Protocol — an arrangement keeping Northern Ireland aligned with EU single-market rules for goods and creating a regulatory border in the Irish Sea — and called a December 2019 general election under the slogan "Get Brexit Done." The Conservatives won an 80-seat majority. The UK formally left the European Union at 23:00 GMT on 31 January 2020, opening an eleven-month transition period during which EU rules continued to apply.

**The Trade and Cooperation Agreement.** Negotiations on the future relationship ran through 2020 to the wire and produced the EU–UK Trade and Cooperation Agreement (TCA), signed on 24 December 2020 and provisionally applied from 1 January 2021. The TCA delivered zero-tariff zero-quota trade in goods but did not preserve frictionless trade — exporters faced customs declarations, sanitary and phytosanitary checks on agri-food, and rules-of-origin paperwork. Services, including financial services, fell largely outside the agreement. The UK left the Erasmus+ programme and the European single market for services.

**The Northern Ireland Protocol and the Windsor Framework.** The Protocol began operating in 2021 and immediately generated political pressure within Northern Ireland: unionist objections to the regulatory border in the Irish Sea led to the Democratic Unionist Party withdrawing from the Northern Ireland power-sharing executive, suspending it for two years. The UK and EU renegotiated the Protocol into the Windsor Framework in February 2023 — replacing parts of the original mechanism with a "green lane / red lane" system distinguishing goods staying in Northern Ireland from those continuing to the EU single market. The Northern Ireland Executive was restored in February 2024 after a long suspension.

**The Conservative interregnum.** Johnson resigned as Prime Minister in 2022 over a series of standards controversies. Liz Truss succeeded him in September 2022; her mini-budget triggered a bond-market crisis and forced her resignation after 49 days — the shortest tenure of any UK Prime Minister. Rishi Sunak governed from October 2022 to July 2024. The Sunak period saw the Windsor Framework agreed and a series of attempts to demonstrate "Brexit benefits" through regulatory divergence; politically the government struggled to recover from the Truss crisis and from sustained dissatisfaction with public-service performance and immigration policy.

**The 2024 Labour landslide.** The general election of 4 July 2024 produced a Labour majority of 174 — the largest since 1997 — with Keir Starmer becoming Prime Minister. The Conservative vote share collapsed to its lowest in modern history, partly to Reform UK on the right and partly to Liberal Democrats in former Conservative seats in southern England. Labour's manifesto position on Europe was explicit: no return to the single market, no return to the customs union, no return to freedom of movement, but a "reset" of the relationship with the EU through selective sectoral cooperation.

**The Starmer reset.** The first eighteen months of the Starmer government have pursued that selective reset. The areas in active discussion include: a sanitary and phytosanitary (SPS) agreement to reduce friction on agri-food trade; a defence and security partnership; an energy-market cooperation framework; and a youth-mobility scheme. A UK–EU summit on 19 May 2025 formalised the political dialogue and set out the agenda. The constraints are clear and self-imposed by both sides: nothing that requires re-joining the single market or the customs union; nothing that re-opens the politically settled Brexit question in domestic UK politics.

**The economic question.** Whether Brexit has materially damaged the UK economy, and by how much, is a contested but increasingly addressed question. The Office for Budget Responsibility's standing assumption is that Brexit will reduce long-run UK productivity by roughly 4 % relative to a counterfactual of continued EU membership, primarily through reduced trade openness. The Bank of England has produced compatible estimates. Critics of these estimates argue that the counterfactual is unknowable and that other shocks (COVID, the 2022 energy crisis) confound the attribution. The defenders argue that the methodology is conservative and consistent with the pre-referendum forecasts of pro-Brexit economists themselves. The OBR's full methodology is in the public record (see Sources).

**Northern Ireland: an ongoing settlement.** The Windsor Framework operates today but is not static. Technical issues — particularly around the "red lane" for goods continuing into the EU, around veterinary medicines, and around parcel deliveries — continue to be negotiated. The political settlement in Northern Ireland depends on the continued operation of the Executive, which depends on the major parties' continued willingness to participate. None of these is permanently settled.

**Distinguishing settled from contested.** The Brexit question is, at the level of the UK's formal status, settled: the UK is not a member state of the European Union and there is no major-party support for re-applying. The questions of what specific selective cooperation is politically possible, of how much Brexit has cost economically, and of how the Northern Ireland settlement evolves, are live. The *Current situation* section above carries the present state of those questions; the *Understand the debate* section lays out where the genuine disagreement is.