The European Commission's chief Brexit negotiator Michel Barnier on Monday called on London to draw up fresh proposals for resolving differences in trade talks before a summit in June.
"Until we reach this agreement, there is a risk,” Mr Barnier said, stressing the need for “rapid progress” at the start of his two-day visit to Ireland where he will meet business leaders on both sides of the 380km open border.
Mr Barnier, addressing reporters in the southern Irish border town of Dundalk, said progress was necessary in early summer before the deadline of final talks in October.
Dublin insists there must be no hard border between north and south, a symbol of the Troubles when more than 3,600 people were killed in three decades of violence between paramilitaries and security forces. The UK has agreed in principle, but negotiators have been vague about how a seamless border would work.
“I think we have to use the time from now to June and from June to October to find this operational solution for Northern Ireland,” Mr Barnier said.
The EU negotiator’s trip got off to a tetchy start. Mr Barnier urged Britain to either reach a border agreement or accept the “backstop” arrangements which would see Northern Ireland align with the EU single market post-Brexit. The fall-back option means Northern Ireland would diverge from the UK on trade, however, an arrangement not acceptable to the Democratic Union Party, which shores up Theresa May’s minority government.
DUP leader Arlene Foster accused Mr Barnier of not understanding Northern Ireland’s unionist culture. Any border solution that pushes Northern Ireland away from the UK will not get DUP support, she said.
“His proposal of us being in an all-Ireland regulatory scenario with a border down the Irish Sea simply does not work. It does not work constitutionally, politically and it certainly does not work from an economic perspective” Ms Foster told the BBC.
Mr Barnier said the DUP leader failed to understand that he represented the EU, not Britain.
“I am the negotiator for the 27. Mrs Foster and some others need to understand that and respect that,” Mr Barnier told a press conference along with Irish Prime Minister Leo Varadkar.
The Irish border will be Britain’s only land border when it leaves the union in March 2019 and it is one of the most difficult challenges given the warring history between north and south.
Dr Graham Gudgin, former adviser to ex-Northern Ireland first minister David Trimble, and Ray Bassett, former Irish ambassador to Canada, argue that it is possible for the UK and Northern Ireland to leave the customs union, avoid a hard border and preserve the 1998 Good Friday peace agreement.
In an article for the British centre-right think tank Policy Exchange, Mr Gudgin and Mr Bassett argue that the most logical option is for Ireland to "work hard on the EU side" to agree to a free trade deal between Brussels and the UK, with no tariffs and a minimum of red tape.
“Ireland should also be lobbying for an arrangement to allow for a mutual recognition regime between the custom services of the UK and the EU. This approach already has the support of the British government. Now is the time to get Brussels to fully sign up,” they write.
Mr Gudgin and Mr Bassett also argue that technology can play a role in ensuring a seamless border and that electronic means already proposed by the UK could be adopted – with some finessing – to enforce customs regulations without infrastructure at the border and without stopping individuals or traders.
Brussels has not yet agreed to London's technological proposals to avoid a hard border, and Prime Minister Theresa May is under pressure at home and abroad to find a fresh solution. The House of Lords passed an amendment to the EU (Withdrawal) bill in April asking ministers to explain steps taken to negotiate Britain's participation in a customs union.
Irish leader Leo Varadkar said Britain’s “approach to negotiations will need to change in some way” if there is to be an agreement.
"Without a solution to the Irish border question, there can be no EU withdrawal agreement," Mr Varadkar added.
Mr Barnier has already said border checks will be unavoidable if the UK leaves the single market and customs union, which allow the EU to operate as one territory without internal borders or regulatory obstacles to trade.
“This is an extraordinary negotiation, very complex, extraordinarily complex and we want to succeed with the UK, not against the UK,” Mr Barnier declared.