UK and EU Brexit negotiators have begun fresh talks in Brussels to attempt to hammer out a compromise on Northern Ireland, almost two years on since the UK left the EU.
If they fail to find a common solution in the row over the Northern Ireland Protocol, the UK has threatened to suspend the treaty on post-Brexit trade arrangements in its province.
This would almost certainly bring retaliatory measures from the EU and possibly a trade war.
"Obviously, there is still quite a big gap. And that’s what we’ve got to work through," UK chief negotiator David Frost said as he entered a lunch meeting with his EU counterpart, Maros Sefcovic.
The European Commission has made proposals to ease red tape on trade between Britain and Northern Ireland but within the framework of the protocol which forms part of the binding EU-UK divorce deal. It wants a deal by Christmas.
The UK wants the treaty replaced with a new agreement, even though it was negotiated by Frost himself and Boris Johnson's government willingly signed up to it.
Brussels has offered to reduce drastically both paperwork and checks on goods sent from Britain to Northern Ireland, a consequence of the fact the territory remains subject to EU rules under the protocol.
These have been welcomed by businesses in Northern Ireland and the British government, but both London and the province's largest party, the Democratic Unionists, say the move is not enough.
The UK is also insisting the EU cede final legal oversight by its top court of any disputes on Northern Ireland trade and instead make them subject to independent arbitration, something the 27-nation bloc is flatly rejecting.
The role of the European Court of Justice (ECJ) is clearly set out in the protocol. But Sefcovic, who visited Northern Ireland again on Thursday, says he has barely heard the issue raised by businesses there.
Fish might also be pushed onto the menu in Brussels, with French fishermen threatening to block ports for what they see as British duplicitousness over licences.
France has said it will take "retaliatory" measures as early as next week if the UK does not grant more licences to French fishermen, Paris has warned. This could include reducing electricity supplies to Jersey, the Channel island which is a UK dependency.
The post-Brexit trade agreement says licences should be granted to European fishing boats to continue to operate in certain British waters if they can prove they were already working there prior to Brexit. But the French and British are arguing over the nature and extent of the evidence required.