By Friday Dublin must reach an agreement with London over the Northern Irish border, or Brexit talks will be derailed.

The Irish government demands a written assurance that the 500-km border will remain “soft,” that is, without a need for checkpoints. The UK argues that such assurances can only be extended if and when Brussels and London have determined the future of their trade relations.

Neither Dublin nor Belfast or London will budge.

Downing Street has made clear on more than one occasion that the UK will leave the Single Market and the Customs Union “as a whole.”

Theresa May has little choice on the matter. In Belfast, the Democratic Unionist Party (DUP) has made clear that it will not accept any deviation of Northern Ireland from the rest of the UK. And Theresa May’s majority depends on DUP parliamentary support.

On Monday, Theresa May and the international Trade Minister, Liam Fox, reiterated that the Irish question can only be addressed in the second phase of Brexit negotiations, once trade relations with the Single Market have been settled.

In Dublin, the Minister of Foreign Affairs and Trade Simon Coveney said that it is not “credible” that the UK will leave the Customs Union and the Single Market and there will be no regulatory divergence on both sides of the Irish border.

Dublin demands either that the UK as a whole or Northern Ireland remain in the Customs Union and the Single Market, moving the Irish border to the Irish Seq. In no uncertain terms, Ireland has made clear that the government will not authorize moving on to trade talks before a guarantee on the border. “We don’t need to use a veto because we have complete solidarity on this issue,” Coveney said.

The DUP leader, Arlene Foster, wrote to all EU leaders on Monday to make clear that Northern Ireland will not deviate from the rest of the UK.  

Speaking to BBC Radio 4 on Monday, the former Irish Prime Minister, Bertie Ahern, noted that smuggling will undermined the Good Friday agreement by providing criminal groups – often linked to militias – a major source of revenue. In any event, it would be hard to avoid setting up checkpoints and creating a hard border, even if only 2% of goods and vehicles passing the border were physically checked.