The EU Agriculture Commissioner Phil Hogan has warned that Brexit talks cannot continue to the next phase until there are concrete guarantees over the Irish border.
Mr Hogan said the issue could be solved by keeping the UK in the customs union and single market - or allowing Northern Ireland to do so.
In a statement, he warned the best possible trade deal available to the UK will fall far short of the benefits of “being in the single market.”
The border is one of three issues that must see “sufficient progress” before the EU will allow talks to move on to discussions on future trade relations.
The Government has consistently warned that there can be no return to a hard border – with both the EU and the UK offering promises that it can be avoided.
The UK has, thus far, failed to provide any concrete proposals for how this may work, and at the EU Summit in Sweden last week, the Taoiseach said the UK must provide a commitment “written down in practical terms” before the talks can move forward.
It has been suggested in many quarters that a border could be avoided if Northern Ireland is given special status to remain in the customs union, even if the rest of the UK does not.
However, yesterday the DUP leader Arlene Foster warned that her party will not support any Brexit deal create barriers to trade between Northern Ireland and Britain.
In an interview with the Observer Newspaper this morning, Mr Hogan said the best solution for all would be for the entire UK to remain in the customs union.
He said it was a "very simple fact" that remaining in the single market and customs union would end the standoff, adding that Ireland will "continue to play tough until the end."
"If the UK or Northern Ireland remained in the EU customs union, or better still the single market, there would be no border issue,” he said. “That's a very simple fact.”
"I continue to be amazed at the blind faith that some in London place in theoretical future free trade agreements (FTAs).
"First, the best possible FTA with the EU will fall far short of the benefits of being in the single market. This fact is simply not understood in the UK.
"Most real costs to cross-border business today are not tariffs - they are about standards, about customs procedures, about red tape. These are solved by the single market, but not in an FTA."
However the fact remains that the staunchest Brexiteers in the British Government and Conservative Party are highly unlikely to accept the proposal – while the DUP will oppose any plan to move the border into the Irish Sea.
In a speech to her party’s annual conference yesterday, DUP leader Arlene Foster said: “We want our border to remain open for people to move freely north and south for work, for education and as tourists.”
“We want to see continued trading across the border in the economic interests of our two countries.”
However, she said the north's most important trading relationship remains with Britain, adding "we will do nothing that puts this at risk in any way."
“We will not support any arrangements that create barriers to trade between Northern Ireland and the rest of the United Kingdom or any suggestion that Northern Ireland, unlike the rest of the UK, will have to mirror European regulations.”
She claimed the border issue can be resolved during talks on the UKs future trading relationship with the EU.