This article is updated regularly as events unfold.
The United Kingdom is due to leave the European Union — an economic and political partnership of 28 countries — bringing to an end 47 years of British membership.
Three and a half years after the UK voted to quit the EU in a referendum, the country's exit is finally on course to take place by January 31, 2020 — following the Conservative Party's emphatic election victory.
However, both sides face a huge challenge to strike a trade deal and address the future relationship before a stand-still transition period ends in December 2020.
Brexit is set to be the most important constitutional shake-up the UK has known since it joined the six-nation European Economic Community in 1973, and represents the first time the European institution has lost a member.
The process plunged the UK into its worst political and constitutional crisis since the Second World War. The country's departure from the EU was repeatedly delayed amid a period of turmoil in the British parliament — which saw Boris Johnson replace Theresa May as prime minister and renegotiate the divorce deal.
The UK voted to leave the EU by 52% to 48% in June 2016. The result has increased strains between the UK's individual countries: England (53%) and Wales (52.5%) voted to leave, whereas Scotland and Northern Ireland voted by 62% and 56% respectively to remain in the EU.
Brexit follows decades of increasing hostility to the European project in the United Kingdom, reinforced in recent years by a rise in English nationalism. Other factors such as austerity and frustration with traditional politics have also come into play. The fallout has highlighted a rift between metropolises, and towns and rural areas, and feeds into a wider debate concerning the role of the nation state and the rise of populism in an age of globalisation.
There is concern, however, that the prolonged and often acrimonious process has shifted attention from major global challenges, not least the battle to contain climate change. For many in Europe, the prospect of an institutionalised rift between the UK and the EU weakens the continent at a time when the likes of America, China and Russia are becoming increasingly assertive.
Latest developments and stories (to January 20):
Brexit beckons on January 31 as Boris Johnson's election gamble pays off
The UK finally broke the long-standing Brexit stalemate following the snap general election on December 12, which brought a crushing victory for Boris Johnson's Conservative Party.
The Tories won a majority of 80 seats, paving the way for the UK to leave the EU by the end of January under the terms of a divorce deal renegotiated this autumn.
EU leaders welcomed the "clarity" brought about by the election result. Brussels agreed to move forward with trade talks with London after it signs off on the Brexit deal. Many in the EU want to keep close ties with the United Kingdom.
However, there has been scepticism over whether the scheduled post-Brexit transition period in 2020 allows enough time to strike a trade deal and work out the future relationship.
The election result also looks set to increased tension within the UK's four nations as Scotland and Northern Ireland saw significant anti-Brexit votes.
Giving legal effect to the divorce deal
The default legal position is that the UK will leave the EU on January 31, 2020 — either under the terms of the negotiated divorce deal if it is ratified, or without an agreement if that doesn't happen.
The deal — a Withdrawal Agreement on the terms of departure, accompanied by a Political Declaration on future ties — needs the approval of the British and European parliaments to take effect.
Once that happens, it will give the force of an international treaty to the divorce terms — which include safeguards for the rights of EU citizens living in the UK, and Britons living on the continent.
Prime Minister Boris Johnson lost no time in bringing legislation before the UK parliament to ensure a smooth exit. Given the ruling Conservatives' healthy majority, the Brexit bill is well on course to pass. However, much related legislation — on matters ranging from trade to agriculture to immigration — also needs to be tabled.
Meanwhile, the European Parliament has warned that its approval for the divorce deal will depend on assurances given, especially by the UK over the rights of EU citizens resident in the country.
Tough trade talks ahead
Once the UK leaves the EU, from February 1 a transition period comes into force under the terms of the exit deal — assuming it is ratified. This will keep arrangements between the UK and the EU largely as they are until it expires on December 31, 2020.
During this time the UK and the EU will turn to negotiating the terms of their future relationship. The British government argues that a trade deal can be struck within this time frame, and the Brexit legislation includes a commitment to rule out an extension of the transition period beyond December 2020.
However, European leaders have repeatedly sounded alarm bells. The EU's chief Brexit negotiator Michel Barnier has said that achieving a comprehensive trade deal in 11 months is "unrealistic". The new European Commission President Ursula von der Leyen has said the UK's imposed deadline leaves "very little time".
How did the Conservatives win the UK general election?
Although the ruling Conservatives had developed a significant lead in opinion polls, the election outcome had been seen as uncertain given a volatile political situation, and after a campaign noted for questionable tactics and large volumes of misinformation.
The Tories — boosted by the decision of the anti-EU Brexit Party under Nigel Farage largely to stand aside — campaigned on a promise to leave the EU by the end of January.
Critics argued that a general election was not the correct way to resolve the UK's Brexit crisis. But the prime minister's campaign slogan of "Get Brexit Done" evidently struck a chord with voters. The unpopularity of opposition leader Jeremy Corbyn also played a part as many traditional Labour seats fell to the Conservatives.
The new parliament looks very different from the last. The election brought a cull of centrist politicians — several of whom had previously left the two main parties accusing them of extremism. Dozens of MPs had previously said they were standing down, amid many complaints over a toxic atmosphere in British politics.
Excluded from voting were many who will nonetheless be affected by the outcome: the UK's estimated three million EU nationals, as well as hundreds of thousands of Britons who have lived abroad — including in EU countries — for over 15 years.
Defeat for "Remain" — but a boost for Scottish and Irish nationalists
The main opposition Labour Party suffered its biggest defeat since 1935, while the pro-EU Liberal Democrats won only 11 seats — despite increasing their share of the vote — as the "Remain" vote was split.
Under Jeremy Corbyn, Labour had said that in government it would renegotiate a Brexit deal which would then have been put to the public in a second referendum. The party tried to highlight domestic issues such as the state of the health service, the impact of austerity, poverty and social injustice.
The Liberal Democrats' campaign pledge to stop Brexit altogether if elected was unpopular with voters, and the campaign brought a decline in support which culminated in defeat and the loss of leader Jo Swinson's seat. She and Corbyn said they would stand down.
The Scottish National Party (SNP) which also campaigned to "stop Brexit", via a second public vote, won the vast majority of seats north of the border with England. It is calling for another referendum on Scottish independence, following a failed attempt in 2014, but Boris Johnson's re-elected government has refused to grant it.
There were also calls for a border poll on the island of Ireland after Northern Ireland elected more Irish nationalists to the UK parliament than pro-British unionists, a first since partition nearly a hundred years ago.
Brexit 'clarity' follows prolonged stalemate
On October 29 the European Council President Donald Tusk confirmed that the EU had formally adopted the latest extension of the UK's membership until 31 January 2020. The UK can leave earlier if the renegotiated divorce deal is ratified.
The delay put paid to Boris Johnson's vow, repeated many times, that the UK would leave the EU on October 31.
It was a blow at the time to the British prime minister, who wants desperately to succeed where his predecessor failed in taking the UK out of the EU — and had said he would meet the Halloween deadline "come what may"... "do or die".
But in the absence of parliamentary approval for his renegotiated deal by October 19, Johnson was obliged by law to seek a delay of three months from the European Union. After being forced to sit out the UK's election drama, some EU leaders said they were pleased that the result delivered some clarity — while warning that a more difficult challenge was still to come in determining the future relationship.
Brexit deal done — but UK bill derailed
The EU and the UK announced on October 17 that they had reached agreement on a revised exit deal. It came on the day of a crucial EU summit and followed a period of intensified talks. The accord was swiftly given the green light by EU national leaders.
The deal alters previously-negotiated arrangements for Northern Ireland, and envisages a clearer break for the UK with the EU than the accord struck by Theresa May.
Boris Johnson became prime minister in late July, but it was early October before his government submitted a detailed proposal for a new divorce deal to Brussels. He then threw out its controversial plan for Northern Ireland to reach a compromise.
A bill to implement the new deal passed its first parliamentary hurdle, but was shelved by Johnson himself when MPs rejected the government's fast-track three-day timetable to get it passed. Many felt far more time was needed to scrutinise measures that will determine the UK's relations with Europe for years to come.
What's in Johnson's new Brexit divorce deal?
The main change from the deal negotiated by Theresa May's government is that in the revised Withdrawal Agreement, the controversial Irish "backstop" contained in the previous accord (see below) — to keep an open border on the island of Ireland — is scrapped.
There are also changes to the Political Declaration on the shape of future relations. The government has signed up to various assurances on future trade competition and other matters — but critics are wary that the commitments may not be watertight.
The new agreement keeps the existing provisions on the key “divorce” issues: settling the UK's financial obligations to the EU, and safeguarding citizens' rights — those of EU nationals living in the UK and Britons in the EU. These will come into force if the deal is ratified.
As with May's deal, if ratified it would also pave the way for a the way for a planned transition period, to come into effect after the UK’s departure and run until the end of December 2020. During this period many existing arrangements would remain in place.
The agreement allows for a two-year extension, which Boris Johnson has ruled out invoking. Critics say the shorter deadline provides nowhere near enough time to sort out a new trade deal and all future EU-UK relations, and avoid an abrupt “cliff-edge” at the end of the transition period.
Irish backstop removed
The border between Northern Ireland (part of the UK) and the Republic of Ireland (part of the EU) – one of the most politically sensitive frontiers in the world – will become the European Union's only land border with the United Kingdom after Brexit. All sides agree this must remain open, but the historically sensitive and complex issue bedevilled the talks.
The backstop was essentially an insurance policy to avoid a hard border — such as border posts — and protect the cross-frontier economy between Northern Ireland (part of the UK) and the Republic of Ireland (part of the EU), post-Brexit. In the absence of a trade deal or an alternative solution, the whole of the UK would remain in a customs union with the EU, while Northern Ireland would be aligned even more closely with EU rules.
Under the new deal, Northern Ireland would leave the EU's customs union with the rest of the UK, which wants to pursue an independent trade policy. But in practice it would follow EU customs rules and be subject to EU oversight.
The North would remain aligned with some aspects of the EU's single market — and apply EU law on VAT (Value Added Tax) rules.
Customs and regulatory checks would not be carried out on the island of Ireland, but at ports — effectively creating a new regulatory divide in the Irish Sea.
The agreement has similarities with an original EU proposal for a Northern Ireland-only backstop — which was rejected by Theresa May's government — but is more complex, and has one key difference in that legally, Northern Ireland would be in the UK customs union.
The accord deals with the issue of Northern Irish consent for these changes: Northern Ireland's assembly would be able to decide on whether to keep the new arrangements — but only four years after a planned transition period.
How important is the Political Declaration on future ties?
Boris Johnson also signed up to a "level playing field" with the EU over issues including state aid, competition, social and workers' rights, the environment and climate change.
However, this engagement is included in the revised Political Declaration on future EU-UK relations — which is legally non-binding — rather than the withdrawal agreement which would have the force of an international treaty. The document provides a framework which could form the basis for a future trade agreement.
Many critics of Brexit argue that negotiations over future ties risk being much more complicated and harder to resolve than the divorce deal. These would begin once the UK has left the EU on agreed terms.
In the original declaration negotiated by the previous UK government, Theresa May envisaged the UK remaining closely aligned to the EU. The new document is causing concern among some Brexit opponents — especially given the Johnson government's avowed intention to diverge from EU rules and forge an independent trading path.
The declaration relates to a future EU-UK economic relationship where the UK opts for a Free Trade Agreement (FTA). But in return for zero tariffs and quotas, the UK makes "robust commitments on a level playing field" to ensure "open and fair competition".
Running parallel to the Brexit saga has been the UK's evolving relationship with the United States, with which Britain hopes to strike a future trade deal. Boris Johnson met President Donald Trump at a G7 summit and admitted talks would be tough. Trade experts say the UK faces a key choice over regulatory alignment: whether to stay close to EU rules to access the European market, or follow American regulation.
Why might December 2020 see another 'no-deal scenario'?
Throughout 2019, the fear for many on both sides of the English Channel was that the UK could "crash out" of the EU without an agreed deal on either the terms of the divorce or the future relationship. In such an event, legal arrangements covering many aspects of everyday life would abruptly cease to apply.
But although a "no deal" exit in January 2020 remains technically possible, the UK election result makes it unlikely. Once ratified, divorce agreement terms on issues such as citizens' rights will take legal effect, as explained above.
The new "no deal" that is being talked about refers not to Britain's exit from the EU — but to a potential failure to reach agreement on future relations.
The formidable challenge of securing a trade deal with the EU in a few months during the transition period — a task that usually takes the bloc several years — means the UK could be staring at another economic "cliff-edge" in 2020.
Failure to secure a trade deal would hit the UK's economy but also those of its closest continental neighbours — and Ireland. It would bring an immediate change in the trading relationship between the UK and the EU.
Other important matters such as cooperation on security and terrorism, education and science risk being left up in the air if no detailed agreement is reached on future EU-UK relations.
Warnings of economic damage and disruption
Many political leaders, institutions, companies and individuals have warned of severe disruption and economic damage on both sides of the English Channel — with the UK being hit worse than the EU.
However, Brexiteers have long dismissed “Project Fear” forecasts and some argue that the UK could survive perfectly well under World Trade Organisation (WTO) rules.
Government documents, published in early September and codenamed "Operation Yellowhammer", confirmed a grim assessment of the potential impact of a no-deal scenario. Based on the government's own preparations for a no-deal Brexit in a "worst case" scenario, they contained warnings of possible food, medicine and fuel shortages.
The heightened uncertainty amid a year of British political turmoil in 2019 twice forced the UK and the EU — as well as people and businesses on both sides of the English Channel — to step up no-deal preparations, as the Brexit process dragged on without formal approval for an exit deal.
Theresa May's government published a series of papers — some updated under her successor — advising UK citizens and businesses on the consequences and how to prepare for no-deal. It said the EU would treat the UK as a "third country", and there would be no agreement on applying arrangements set out in the exit deal.
British economic sectors reliant on close, smooth arrangements with Europe have warned of the dangers of new costs and restrictions being imposed overnight. Among those sounding alarm bells are manufacturing industries — including the car industry, food and drink, chemicals and pharmaceuticals – as well as aviation, the health service, tourism, and financial services. There have also been warnings over farming and fishing — despite strong support for Brexit from within these two sectors.
In August 2019, after the Bank of England lowered its growth forecast for the UK post-Brexit, its governor Mark Carney warned that in the event of no deal the economy would suffer an instant hit, prices would rise and the pound would fall, and even large profitable industries would become "uneconomic".
In April a leaked letter by the government's most senior civil servant warned of an economic recession, food price rises, a severe impact on Britain's security services, police forces and legal system, and a return to direct rule by the UK government in Northern Ireland. In early August a leaked government document contained similar warnings.
In June, the same civil servant, Sir Mark Sedwill, said government and public services were in "pretty good shape" to cope with a no-deal Brexit at the end of October. He added that in the private sector the level of preparedness varied from sector to sector.
In November 2018, two major reports by the UK Treasury and the Bank of England assessed the potential damage to the British economy of various Brexit scenarios.
In its assessment of EU preparations for no-deal, the UK House of Commons Library describes the Commission's programme as one of "damage limitation" to protect the EU27 countries.
How did Boris Johnson reach a revised deal with the EU?
In a nutshell, Boris Johnson made major concessions over Northern Ireland.
Gone are the UK's proposals — much vaunted by Brexit supporters — for "alternative arrangements" including technological solutions to keep an invisible border. Instead, Johnson has agreed to a different status for Northern Ireland compared to the rest of the UK — accepting a plan very close to one the EU originally proposed.
The EU also gave ground, re-opening the withdrawal agreement it had always said was sacrosanct. Dublin and Brussels agreed to replace the controversial Irish border backstop that had plagued Brexit talks for months, and opened the door to a possible time-limit on border safeguards with the new consent mechanism.
From near-breakdown to breakthrough
Ahead of the key EU summit on October 17-18, hopes were suddenly revived that agreement might — just — be achievable between the UK and the EU. The positive mood followed a meeting between UK Prime Minister Boris Johnson and his Irish counterpart Leo Varadkar.
The details were kept under wraps, but Brussels responded positively to new compromise proposals from London on customs arrangements on the island of Ireland. Ten days earlier, talks between London and Brussels had all but collapsed amid an outburst of acrimony, with both sides blaming each other.
However, Johnson's change of tack came at a price: Northern Ireland's Democratic Unionist Party (DUP), until then an ally of the government, said it could not support proposals that would create a "border in the Irish Sea".
Arrangements for Northern Ireland were a key sticking point throughout negotiations ever since the UK triggered the formal Brexit process in March 2017. Behind the details over trading arrangements are fundamental questions concerning identity. The possibility of new borders — between Northern Ireland and either the Irish Republic, or Great Britain, or both — is hugely problematic in a region with a troubled past.
Previous UK plan gets cool response
After months of political and constitutional turmoil in the United Kingdom, the British prime minister finally submitted a Brexit plan to the European Commission in early October. But it quickly became clear that huge gaps remained in their respective positions.
Boris Johnson’s original plan amounted to a radical overhaul of the divorce agreement negotiated by Theresa May's government. The Irish border "backstop" — the main sticking point throughout the talks – would be stripped out.
Northern Ireland would leave the EU’s customs union along with the rest of the UK — but would remain partially aligned to EU single market rules, subject to approval by Belfast every four years.
The prime minister’s assurances over customs checks in the politically sensitive region failed to convince EU leaders, citing a 1998 peace accord. The proposals over the single market and consent also caused alarm — not least among many in Northern Ireland’s business and farming communities.
'Get Brexit done': new drive for EU exit door as Johnson becomes PM
The UK's stance towards Brexit took on a distinctly harder edge when Boris Johnson entered Number 10 Downing Street in late July, raising the likelihood that the country would leave the EU without a withdrawal deal.
The former foreign secretary and London mayor took over the reins after winning the Conservative Party leadership contest. He signalled immediately a reinvigorated drive to take the UK out of the EU on October 31, "no ifs or buts" — he also used phrases such as "come what may" and "do or die" — and appointed prominent Brexiteers to key posts in his new cabinet.
His stance won strong support among Conservative Party members, although many experts say a no-deal Brexit would bring only economic chaos and a new era of uncertainty.
Upon taking office, the new prime minister immediately issued a demand for the Irish backstop to be removed from the negotiated withdrawal deal. This was quickly rebuffed by the EU. Johnson followed up with a formal plea in August, arguing that the backstop was anti-democratic and inconsistent with UK sovereignty.
The prime minister said flatly that he would not extend Brexit — he would rather be "dead in a ditch" — insisting that "the UK will come out anyway" even if no deal was struck.
The summer and autumn of 2019 saw the UK government significantly ramp up its no-deal preparations — since stood down — with more funds promised. The Conservative conference in Manchester had a new slogan, “Get Brexit done” — which has echoes of the “take back control” rallying cry of the “Leave” campaign during the 2016 referendum campaign.
In the end Boris Johnson was forced to compromise over Northern Ireland to win a revised deal. UK law forced the prime minister to seek a Brexit delay from the EU, which was duly granted.
Government v MPs: constitutional storm as parliament suspension ruled unlawful
The UK’s new prime minister suffered a humiliating defeat when the country’s highest court ruled that his government had acted unlawfully in early September by suspending parliament for five weeks.
The 11 judges in the Supreme Court ruled unanimously that the decision to prorogue parliament unlawfully prevented it from carrying out its constitutional role without good reason, and was null and void.
Boris Johnson argued at the time that the move had nothing to do with Brexit, and was standard procedure to allow the government formally to set out its agenda in a new parliamentary session.
The government’s opponents had argued the prorogation was intended to muzzle them over Brexit and ensure the UK left the EU on October 31.
The court’s ruling represents a significant check on executive power by the judiciary, and has severely tested the United Kingdom’s unwritten constitution. The country is deeply divided not just over its future in Europe, but also over the nature of its democracy — with defenders of parliamentary representation pitted against supporters of "direct democracy" as embodied by the EU referendum.
Theresa May's Brexit delay brings European election electroshock
Johnson's arrival in No 10 Downing Street followed a prolonged period of turmoil in British politics. This came to a head when Theresa May — who failed to get her EU divorce deal through parliament — became the latest in a long line of Conservative prime ministers to be brought down by Europe.
In the wake of the repeated parliamentary defeats for the EU divorce deal, the House of Commons twice forced the British government to seek to delay Brexit. EU national leaders met for a special European Council summit on April 10 and agreed to a six-month "flexible extension" to the UK's departure from the bloc, with a new exit date set for October 31 — or earlier if its parliament approved the original withdrawal deal.
But relief at avoiding a disruptive no-deal exit was tempered by renewed uncertainty and frustration for businesses and people — especially for EU and UK expats.
The extension of the UK's EU membership also forced the country to take part in the European Parliament elections in May — and send 73 newly-elected MEPs to Strasbourg in July.
Nigel Farage's new Brexit Party, which advocates leaving the EU without a formal agreement, came top of the European vote. But there was a strong showing from pro-EU parties, in particular, the Liberal Democrats, who want to reverse Brexit altogether.
Britain's two main parties — the Conservatives and the Labour opposition — were severely punished by voters. Many Conservatives are furious at the failure to “deliver Brexit”, while Labour was accused of sitting on the fence.
The results indicated that opinion in the UK had become still more polarised over Brexit, confirming the results of surveys which suggest that people were essentially entrenched in two camps — those who wished to remain in the EU, and those who were determined to leave, even with no deal.
Why did the UK parliament repeatedly reject Theresa May's deal?
Theresa May's withdrawal deal was negotiated by London and Brussels over an 18-month period and approved by the 27 other EU governments in November 2018. It was rejected three times by the UK parliament between January and March 2019 — leading to May's resignation and her replacement by Boris Johnson.
The former prime minister insisted her negotiated withdrawal agreement was in the national interest and there was no viable alternative. She argued that it delivered on the referendum result: an end to free movement, an end to huge UK payments to the EU, and an exit from the unpopular EU structures on farming and fishing.
However, the agreement brought hostility from both supporters and opponents of Brexit. In parliament, an alliance of forces resulted in the successive defeats for the government.
The main Labour opposition said the deal did not meet its six Brexit tests.
Derailed by the backstop
To guarantee an open border, the backstop envisaged the UK remaining in a "single customs territory" with the EU, in the absence of a free trade deal or an alternative solution. It proved to be a major stumbling block in the negotiations.
Eurosceptic critics, including the Conservative anti-EU European Research Group (ERG), suspected it would have kept the UK strapped permanently to EU trade policy. EU sources pointed out that the UK-wide mechanism in the withdrawal agreement was included at the UK’s request, to avoid splitting off Northern Ireland from the rest of the UK.
Northern Ireland's Democratic Unionist Party (DUP), on whose support the May government depended, has always vehemently opposed any move it believes might separate Northern Ireland from the rest of the United Kingdom. Under the backstop, as set out in May's deal, Northern Ireland would stay aligned to some EU rules.
Revisions fail to stop defeats
As the clock ticked down towards the original March 29 deadline, the UK and the EU said they had agreed a revised Brexit deal following weeks of deadlocked talks between London and Brussels.
EU27 leaders had refused to alter the text of the withdrawal agreement. But Theresa May said she had secured legally-binding changes over the backstop’s application. The British parliament had voted to seek “alternative arrangements”.
The parliamentary deadlock prompted moves by MPs from different parties to wrest control of the Brexit process and allow a series of "indicative votes" to explore alternative solutions to the government's deal. But there was no majority for any particular solution, other than an opposition to no-deal.
Theresa May's Brexit battles
Theresa May always struggled to keep the pro and anti-European wings of the Conservative Party on board with her Brexit plans.
Her doomed UK-EU divorce deal represented a compromise. But the blurring of several of her so-called "red lines" on the limits of EU power sparked fury within her divided Conservative Party. As negotiations with Brussels brought more UK concessions, a string of government resignations followed.
After the 2017 general election, which left the Tories severely weakened in parliament, hostility amid their own ranks to any moves towards a "softer" Brexit restricted May's room for manoeuvre. Eurosceptics including the DUP strongly opposed her Brexit plan and the subsequent agreement, with many calling for the UK to leave the EU with no deal.
Equally, several pro-EU MPs also opposed a deal which, in their view, would leave the UK worse off than it had been inside the bloc. Some joined calls from opposition parties for a second referendum.
Amid the parliamentary deadlock in early 2019, pressure from Tory Europhiles obliged the prime minister to open the door to a Brexit delay — and engage in cross-party talks, which collapsed after a few weeks.
Theresa May's fate was sealed after she revealed a fourth plan for getting her thrice-rejected Brexit deal through parliament. She tweaked the legislative package and crucially opened the door to a possible confirmatory referendum — a move which angered many in her party and sparked another government resignation.
Why is the UK so torn over Europe?
The United Kingdom's place in Europe — and vice-versa — is an issue that arguably was never properly resolved after the Second World War, and has been brought to the fore by Brexit.
Many in the UK, especially in England, have always been sceptical of the political project revered by many on the continent. The antagonism towards the EU that surfaced during Margaret Thatcher's premiership in the 1980s has been followed by decades of hostile media coverage, especially in British tabloids.
At the heart of the debate in the UK is the balance to be struck between two objectives: a desire for independence, sovereignty and autonomy against the need to retain access to European markets, which, the EU has always insisted, means adhering to EU rules.
The turmoil in the British domestic political scene has cut across party lines. Internal party divisions have affected both the UK government and opposition.
The ruling Conservative party has long been riven between Eurosceptic and Europhile factions. The main Labour opposition has seen tension between its largely pro-EU membership and a leadership more inclined to deliver Brexit. Both parties have been damaged by the issue.
In early 2019, the Tories in particular haemorrhaged support to the new hardline Brexit Party. Meanwhile, both Conservatives and Labour suffered defections of some MPs to a new pro-EU centrist party — since renamed "The Independent Group for Change" — for reasons that included their leaders' stances on Brexit.
A history of UK-EU tension
Check out our series on the history of the United Kingdom's complicated relations with the European Union:
How does the European Union work?
The EU originally developed after World War Two, with the aim of promoting economic co-operation and trade between countries to stop them from going to war again. Its members' economies are now integrated around a single market allowing the free movement of goods, people, services and capital.
Nineteen of the 28 member states use a single currency, the euro. The EU has its own institutions and passes laws affecting many issues across the union.
It highlights the benefits of membership as securing peace, promoting freedom and prosperity as part of the single market, safeguarding food and environmental standards, consumer benefits, protecting human rights, and enhancing Europe's global power.
The European Council is led by its president and is made up of the national heads of state or government, as well as the president of the Commission. It sets the EU's overall political direction but has no law-making powers.
Read more: What does the European Council do?
The European Parliament is the EU's law-making body, is directly elected by EU citizens, and represents them.
Read more: What does the European Parliament do?
The European Commission promotes the EU's general interest. It is made up of Commissioners, one from each member state, nominated by national governments. It proposes and enforces laws and implements EU policies and its budget.
Read more: What does the European Commission do?