The European Union and the United Kingdom continue to be at loggerheads over the Northern Ireland Protocol, the most contentious element of the Brexit agreement.
In the latest twist of the political saga, the British government has announced its intention to table legislation that would alter certain elements of the protocol, ignoring repeated pleas from Brussels and Dublin to avoid unilateral changes.
But why is the protocol so controversial?
The protocol is a special arrangement that ensures the land border between Northern Ireland -- which is part of the UK, and the Republic of Ireland, which is an EU member state -- continues to be invisible and respects the peace deal that put an end to decades of sectarian violence.
Under the scheme, Northern Ireland follows EU customs rules, remains part of the Single Market for goods and applies EU law on VAT (Value Added Tax) in order to avoid border checks between the two sides.
The provisions have been welcomed by the Nationalists, who advocate closer ties with Ireland and the EU, but have enraged the Unionist movement, who complains the protocol has created an unnecessary border in the Irish Sea and effectively separates the province from the rest of the UK.
The latest election to the Northern Ireland Assembly delivered a clear pro-protocol majority and brought the power-sharing executive to a standstill.
Meanwhile in London, the government of Prime Minister Boris Johnson says the arrangement needs to be re-negotiated because it hurts the local economy and undermines the east-west relationship.
Brussels hit back and insists the protocol is the only viable alternative to a hard border and that any adjustment should be made within the existing framework.
The long-lasting controversy has raised fears of a trade war but the political crisis runs much deeper.
Watch the video above to learn more about the Northern Ireland Protocol.