The agreement to revise the Northern Ireland protocol, part of the Brexit deal, sets out trade rules for the province, is on the verge of a deal between the UK and the EU.
Rishi Sunak will hold face-to-face talks with the European Commission President Ursula von der Leyen in the UK on Monday as they try to finalise a deal.
Northern Ireland is part of the EU's single market for goods, under the terms of the protocol agreed by Boris Johnson. An open trade border on the island of Ireland is in effect created, but in effect a sea border has been created. Products arriving into Northern Ireland from the rest of the UK are subject to checks and controls.
The deal has resulted in political instability in Northern Ireland after the Democratic Unionist party withdrew from the Stormont assembly in protest at checks on arriving goods. It disagreed with the continuing role of the European Court of Justice ECJ in the region.
Loyalists have expressed opposition to the protocol and warned that it could destabilise peace in the region.
What are the rules for goods moving across the land border before and after Brexit?
Before the EU's rules, it was easy to transport goods across the border because both sides followed the same rules. After the UK left, special trading arrangements were needed because Northern Ireland has a land border with the Republic of Ireland, which remains part of the EU.
The EU has strict food rules and requires border checks when certain goods, such as milk and eggs, come from non-EU countries.
Why can't the UK and the EU stop checking the land border?
It was feared that cameras or border posts could lead to increased republican activity and a breakdown of the political consensus. During the Troubles, Republican groups attacked border posts.
They arrive in Northern Ireland and can be moved to Ireland under the current agreement. The UK wants goods entering Northern Ireland to be split into two different lanes, green for those going just to Northern Ireland and red for those destined for Ireland.
The green lane will reduce the need for customs paperwork, which is a key issue for business. There is the question whether the UK government will continue funding the trader support service, which helps with administration needs.
What are the sticking points?
There have been several. Will companies have to be registered as trusted traders to join the green lane? Which companies will qualify for trusted trader status? There is an ongoing dispute over online shopping: will Northern Irish customers have to sign a customs declaration in future if they buy goods from outlets in Great Britain?
The EU has asked for the ECJ to settle any future disputes, while the UK wants little involvement, according to reports.
Will there ever be a deal on the protocol?
Sunak's problems may be just beginning, depending on who backs the deal. Will the DUP, the largest unionist party in Northern Ireland, give its blessing? Will Johnson, who has already warned about the deal, signal his support?