Boris Johnson will later publish plans to scrap parts of the post-Brexit deal he struck with the EU in 2020. The PM wants to change the Protocol section of the deal to make it easier for some goods to move between Britain and Northern Ireland. But the EU is against the move, saying it would break international law.
The UK insists its proposals - to be set out in a parliamentary bill - are legal and will secure the future of the United Kingdom.
The two sides agreed the Protocol as they strived to maintain peace in Ireland - including the open Irish border - following Brexit.
The Republic of Ireland is still part of the EU’s single market for goods and services, which the UK has left.
Rather than impose a hard border - involving checks on goods and people moving between Northern Ireland and the Irish Republic - the protocol introduces checks on some goods travelling from from Great Britain (England, Scotland and Wales) to Northern Ireland.
The Democratic Unionist Party (DUP), which won the second-most seats in the recent Northern Ireland Assembly elections, argues this creates a divide that could lead to the break-up of the UK.
It is refusing to set up a new ruling Northern Ireland executive with Sinn FĂ©in - which won most seats in the elections - until changes are made to the protocol.
The UK government, despite signing up to the agreement in January 2020, has also raised concerns, prompting the publication of its bill later on Monday.
Northern Ireland Secretary Brandon Lewis said he was confident it would be lawful for the UK to make changes to the protocol without the EU being involved, and that he expected the DUP to form an executive with Sinn FĂ©in after the bill was published.
Presumably there’s a problem but I’ll leave the explanation/interpretation to Brexit experts.