Britain is warning that it will move to tear up parts of the Northern Ireland Protocol unless Brussels caves in to its demands to renegotiate the Brexit treaty.
Here we tell you everything you need to know about the Protocol, how Boris Johnson wants to change it and whether or not the UK and EU are headed for a trade war.
What is the Northern Ireland Protocol?
The Northern Ireland Protocol is part of the Brexit Withdrawal Agreement and was negotiated in 2019.
It is the treaty that created the Irish Sea border between Britain and Northern Ireland.
It means that Northern Ireland continues to follow about 300 EU rules after Brexit but it also grants the country a unique dual access to both the EU and UK markets.
Why is it important?
The Protocol prevents the need for a hard border on the island of Ireland, which would be highly controversial because of The Troubles.
The EU carries out checks on non-EU goods and animals entering its territory to ensure they meet its rules and standards.
Moving checks on non-EU British goods to the Irish Sea means the border controls do not have to be carried out at the invisible frontier between Northern Ireland and Ireland.
So what’s the problem?
Unionists fear the Protocol is driving a wedge between Northern Ireland and the rest of the UK.
The DUP claims the checks are driving up the cost of living but this is disputed by other parties in Northern Ireland, which claim the country’s special status in the Single Market has shielded its economy.