The UK would have to give up on its plans for free-trade deals with China and the USA under such an agreement, the EU's chief negotiator insisted, but otherwise a customs and regulatory border within the territory of Britain will have to be erected.
Mr Wilson, whose party now props up Theresa May's government, said that while the Prime Minister is saying she will not accept any break-up of the United Kingdom his party was anxious about recent briefings that the Conservatives may agree to EU demands for Northern Ireland to remain inside the customs union after Brexit to prevent a hard border in Ireland.
Barnier said Brexit would trigger the need for customs, Value-Added Tax and compliance checks with EU standards between Ireland and Northern Ireland in the event that a planned "backstop" were triggered because a future EU-UK trade deal was not sufficient in itself to ensure the land frontier was not a "hard border".
LEAVE voters in Northern Ireland regard sacrificing the peace process as an acceptable price for Brexit, new research claims.
The BBC and Sky, without citing sources, reported that the DUP could vote against the budget on October 29 if a deal meant new barriers between the British province and the rest of the United Kingdom.
The European commission official conceded that the EU plan for the province would involve "administrative procedures that do not exist today for goods travelling to the Northern Ireland from rest of the UK", with checks on live animals increasing tenfold.
But he said checks of animals and animal-derived products would still have to take place on the border and cover all of that trade. But he stressed: "Brexit was not our choice".
"The future relationship itself might mitigate the checks and even make some unnecessary".
"If the Government is putting these proposals into the public domain to test the water, our advice is to get its toe out quickly or it is going to get burnt", he said.
The radical move is understood to be one of the options being considered by the DUP if attempts to nail down a deal with Brussels include any proposals that would leave Northern Ireland being treated differently to the rest of the UK.
"If we stay on our current trajectory we will go into the next election with the government having delivered none of the benefits of Brexit, with the country reduced to being a rule-taker from Brussels and having failed to deliver a number of manifesto promises and on the Lancaster House speech", he writes.
But Foster refused to consider such a compromise on Tuesday, saying: "What we said to Barnier is checks of themselves are symptomatic of something different, so we only need checks if Northern Ireland is following a different regulatory regime to the rest of the UK". "Michel Barnier and his team are working day and night to reach a deal, but we are not there yet", he said.