Brexit day will transform the UK's relationship with Europe, shift the country's place in the world and herald a new era in international relations. But little to nothing will immediately change.
The UK's post-Brexit transition period will pick up where the country's EU membership left off, offering a temporary safe harbour while Brussels and London haggle over their long-term relationship.
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During that 11-month spell, the UK will keep many of the benefits and obligations of being in the EU: British nationals will no longer be EU citizens, but they will be able to travel around the union as freely as before; British members of the European parliament will have packed their bags, but the UK will remain a fully integrated part of the single market.
The realities of Brexit will come sharply into focus as the clock ticks down to the end of this year, when the transition period will expire.
What actually happens on February 1?
The UK will enter a twilight period during which it will continue to apply and be bound by all EU laws but will be ejected from the EU's political institutions: no more MEPs, no more British seat at the EU leaders' table, no more UK voice on the boards of the union's myriad technical agencies.
Britain will have zero say over the EU rules that will still apply to the country for the next 11 months. The European Commission will have the power to investigate breaches of the bloc's laws, and the European Court of Justice will have the power to impose fines. The UK will contribute to the EU budget.
UK nationals that have joined the European civil service will have the right to work in it for the rest of their careers. Britain's diplomatic presence in Brussels — known as the UK Permanent Representation to the EU — will be rebranded and British officials' access to EU premises and information will be sharply curtailed.
British diplomats will need to apply for permission even to enter the Brussels institutions' bars and cafés.
What does it mean for citizens?
British and EU citizens will continue to benefit from free movement during the transition period.
After the transition period, Britons living in the 27 EU member states will have their residency rights safeguarded, subject to completing whatever administrative procedures are imposed by the national government.
It is up to each EU country to decide how to carry out that bureaucratic exercise, including whether to create a new type of residence status for UK nationals. EU27 countries have to provide a digital residence document to those with the right to remain.
The divorce deal does not grant British expats full freedom of movement rights within the union. It guarantees rights for UK citizens in the EU27 country where they reside.
This means that a British national living in, for example, Portugal, will not necessarily be able to move to Poland to take up a new job as easily as an EU citizen could. But the European Parliament has urged that UK citizens living in the EU should be granted free movement rights.
What about EU nationals living in the UK?
The 3 million EU citizens resident in the UK have until June 2021 to register for Britain's settled status scheme, which allows them to stay in the UK with existing rights after Brexit. The scheme is open to people who have been living in the country for at least five years.
Those who have not been there long enough can apply for pre-settled status, which grants the right to live and work in Britain for up to five years. To be eligible, someone needs to arrive in the UK before the end of the transition period that runs out at the end of December 2020.
From the start of 2021, EU citizens coming to the UK may need visas and work permits if they plan to build a life there. Britain and the EU have said they want to put in place a visa-waiver scheme for short stays of up to 90 days.
What are the implications for business?
Free movement of goods will continue during the transition period. But Britain will no longer be represented in the crucial technical work the EU carries out to decide which products can be sold in its market and under what conditions.
The European Chemicals Agency, for example, has the power to decide whether a new substance is safe for consumers, while the European Banking Authority sets key rules that affect compliance costs for financial services.
Brexit day also marks the start of a ticking clock for business. They have no idea what awaits them after the end of this year, because the UK and EU have yet to negotiate a trade deal. Whatever is finally agreed, there will be a hard border for trade in goods between Britain and the continent that has not existed for decades.
That puts pressure on business to adjust supply chains, relocate operations, and analyse costs.
Written by: Jim Brunsden and Sam Fleming
© Financial Times