The UK will no longer be a member of the European Union (EU) after 23:00 GMT on 31 January 2020.

For those not following every twist and turn, this is what you need to know.

What is Brexit?

Brexit - British exit - refers to the UK leaving the EU.

A public vote (known as a referendum) was held in June 2016, when 17.4 million people opted for Brexit. This gave the Leave side 52%, compared with 48% for Remain.

What is the European Union?

The EU is an economic and political union involving 28 European countries. It allows free trade, which means goods can move between member countries without any checks or extra charges. The EU also allows free movement of people, to live and work in whichever country they choose.

The UK joined in 1973 (when it was known as the European Economic Community) and it will be the first member state to withdraw.

What happens after Brexit day?

After the UK formally leaves the EU on 31 January 2020, there is still a lot to talk about and months of negotiation will follow.

While the UK has agreed the terms of its EU departure, both sides still need to decide what their future relationship will look like.

This will be worked out during the transition period (which some prefer to call the implementation period), which begins immediately after Brexit day and is due to end on 31 December 2020.

During this 11-month period, the UK will continue to follow all of the EU's rules and its trading relationship will remain the same.

Seven things that will change after Brexit day

What needs to be agreed?

The transition period is meant to give both sides some breathing space while a new free trade agreement is negotiated.

This is needed because the UK will leave the single market and customs union at the end of the transition. A free trade agreement allow goods to move around the EU without checks or extra charges.

If a new one cannot be agreed in time, then the UK faces the prospect of having to trade with no deal in place. That would mean tariffs (taxes) on UK goods travelling to the EU and other trade barriers.

Aside from trade, many other aspects of the future UK-EU relationship will also need to be decided. For example:

Law enforcement, data sharing and security

Aviation standards and safety

Access to fishing waters

Supplies of electricity and gas

Licensing and regulation of medicines

Prime Minister Boris Johnson insists the transition period will not be extended, but the European Commission has warned that the timetable will be extremely challenging.

What is the transition period?

Brexit: What happens next?

What is the Brexit deal?

The transition period and other aspects of the UK's departure were agreed in a separate deal called the withdrawal agreement.

Most of that was negotiated by Theresa May's government. But after Mr Johnson replaced her in July 2019, he removed the most controversial part - the backstop.

Your guide to Brexit jargon

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Brexit day Customs plan Divorce bill Settled status Transition period WTO rules

The backstop was designed to ensure there would be no border posts or barriers between Northern Ireland and the Republic of Ireland after Brexit.

If needed, it would have kept the UK in a close trading relationship with the EU.

Under Mr Johnson's deal, a customs border will effectively be created between Northern Ireland and Great Britain. Some goods entering Northern Ireland from Great Britain will be subject to checks and will have to pay EU import taxes (known as tariffs).

These would be refunded if goods remain in Northern Ireland (ie are not moved to the Republic of Ireland).

Mr. Johnson has removed the backstop, replacing it with new customs arrangements for Northern Ireland

Supporters of the new customs arrangement say it will allow the UK to negotiate its own trade deals with other countries - something that would not have been possible under the backstop.

The rest of the withdrawal agreement is largely unchanged from the one negotiated by Mrs May. This includes:

The rights of EU citizens in the UK and British citizens in the EU (which will remain the same during the transition)

How much money the UK is to pay the EU (estimated to be down to about £30bn)

Why did Brexit take so long?

Brexit was originally meant to happen on 29 March, 2019, but the deadline was delayed twice after MPs rejected the deal negotiated by Mrs May, the prime minister at the time.

Many Conservative MPs and the DUP (the government's then ally in Parliament) were unhappy with the backstop - arguing that the UK could remain trapped in the arrangement for years with no way out.

After MPs voted down the deal for a third time, Mrs. May resigned.

Mr Johnson needed a Brexit extension of his own after MPs failed to get the revised deal passed into law.

This led to the new deadline of 31 January 2020. (BBC)

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