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The UK is no longer a member of the European Union (EU), but that's not the end of Brexit.

UK and EU officials are trying to agree how their future relationship will work.

Why is Brexit still being talked about?

Even though Brexit happened on 31 January 2020, both sides still need to work out the rules for their new relationship. This includes everything from trade, immigration, aviation, security and access to fishing waters.

These rules have to be negotiated and signed off by the EU and UK Parliaments by the end of the year.

Prime Minister Boris Johnson says an agreement on trade must be done by 15 October - if the new relationship is going to be ready in time.

Image copyright Getty Images Image caption Boris Johnson campaigned on a pledge to "get Brexit done" during the 2019 election

But didn't the UK already leave the EU with a deal?

Yes, the UK did leave the EU on 31 January 2020 with a deal called the withdrawal agreement.

However, this deal only set out the process of how the UK would leave the EU, not the future relationship. It covered areas like:

Citizens' rights

How to stop checks along the Irish border

The UK's financial settlement.

Negotiations on the future UK-EU relationship were always intended to be held after Brexit day and during the transition period.

The transition is an 11-month phase which started immediately after Brexit day. It was designed to give both sides breathing space to negotiate their future relationship.

During this time, the UK still follows EU rules and trade between the two is the same as before.

The transition period ends on 31 December 2020 and the deadline for extending it has now passed.

Image copyright EPA Image caption Talks have been taking place via video link due to the coronavirus pandemic

What happens if there's no trade deal by 31 December?

When transition ends, the UK will automatically drop out of the EU's main trading arrangements (the single market and the customs union).

The single market means that countries share the same rules on product standards and access to services, whereas the customs union is an agreement between EU countries not to charge taxes (tariffs) on each other's goods.

If a new trade deal is not ready then tariffs and border checks would be applied to UK goods travelling to the EU. The UK could also do this to EU goods, if it chose to.

Tariffs would make UK goods more expensive and harder to sell in the EU, while full border checks could cause long delays at ports.

Failure to reach a deal would also result in the UK service industry losing its guaranteed access to the EU. This would affect everyone from bankers and lawyers, to musicians and chefs.

Even if a trade deal is reached, it would not eliminate all checks - so UK businesses will need to prepare.

As well as trade, other aspects of the future relationship - such as immigration rules, fishing access and security cooperation - also need to be signed off. If not, then no-deal plans will be required in these areas for 1 January 2021 onwards.

What about the Irish border?

Following Brexit, the 310-mile border between Northern Ireland and the Republic of Ireland is the only land border between the UK and the EU.

All sides wants to avoid border checks given the previous history of conflict. However, finding a solution proved very difficult during the negotiations.

Theresa May, the previous UK prime minister, came up with a plan called the Irish "backstop". However, she was forced to resign after many of her MPs argued her deal would have kept the UK too closely tied to the EU.

In October 2019, Boris Johnson, Mrs May's successor, scrapped the backstop and replaced it with the Northern Ireland (NI) protocol.

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

Under the NI protocol, which will start on 1 January 2021, Northern Ireland will continue to follow some EU rules - making border checks unnecessary.

However, the arrangement will mean that certain goods arriving in Northern Ireland from other parts of the UK (England, Scotland and Wales) will need to be checked to ensure they comply with EU standards. If any taxes (tariffs) need to be paid, they will be refunded if the goods remain in Northern Ireland and there is no onward movement to the Republic of Ireland.

In September 2020, the UK government said it was seeking to change parts of the NI protocol by introducing a new law in Parliament. The UK government says this is needed in order to clarify parts of the protocol in order to avoid disruption on 1 January.

The UK government has acknowledged that its proposal would break international law in a "very specific and limited way".