Democratic Unionist Party leader Arlene Foster has condemned the Brexit legal text produced by Brussels as “constitutionally unacceptable” and potentially “catastrophic” for Northern Ireland.
MPs from her party challenged Theresa May about the issue in the Commons, prompting the Prime Minister to insist that she could not agree to the terms of the EU’s text.
On the crucial issue of the Irish border, the draft text spells out in detail how the principle of “regulatory alignment” agreed in December would be implemented if the UK fails to find technological or diplomatic solutions to keeping the border open.
If such solutions are not found, the draft text states, “the territory of Northern Ireland, excluding the territorial waters of the United Kingdom … shall be considered to be part of the customs territory of the (European) Union”.
It suggests that EU and UK customs authorities should jointly oversee movements between Northern Ireland and the British mainland, while Europe would retain control over aspects of taxation and state aid in the six counties.
Ms Foster said: “EU draft text is constitutionally unacceptable and would be economically catastrophic for Northern Ireland.
“I welcome the Prime Minister’s commitment that HMG will not allow any new border in the Irish Sea.
“Northern Ireland must have unfettered access to GB market.”
At Prime Minister’s Questions, Mrs May said the EU’s text would “threaten the constitutional integrity of the UK” and “no UK prime minster could ever agree to it”.
Ukip’s interim leader Gerard Batten said: “The EU is trying to divide Northern Ireland away from the UK and attempting to undermine and reverse the referendum decision.”
He said the European Commission “shall not be allowed to annex Northern Ireland or put a disruptive hard border”.
But Ireland’s Foreign Minister Simon Coveney said the document gave a “necessary legal provision” to maintain the same trade and customs rules in Northern Ireland in the event that no deal can be struck between the EU and UK.
Mr Coveney added: “This is very much a default and would only apply should it prove necessary.
“This is about delivering on our shared objectives of protecting the Good Friday Agreement and the gains of the peace process, no less, no more.”
Shadow Brexit secretary Sir Keir Starmer said: “The EU-UK Government war of words needs to end.
“There can be absolutely no deviation from the solemn commitments made to Northern Ireland at the end of the first phase of Brexit negotiations. That means no hard border or any agreement that would undermine the Good Friday Agreement.
“Theresa May’s failure to offer any viable solution to the border in Northern Ireland has come back to haunt her.”
TUC general secretary Frances O’Grady urged Mrs May to stand up to the “reckless” demands of “hardliners” in her party, saying: “The draft text would deliver the Prime Minister’s promise of no hard border in the island of Ireland after Brexit.
“Now she must face down the hardliners in her party, and put all options for a final deal back on the negotiating table.
“That’s the best way to protect jobs, rights at work and the Good Friday Agreement.”
Labour MP Chuka Umunna, who supports the pro-EU Open Britain campaign, said: “The Brexit negotiations have reached crisis point because the Government has failed to provide any workable, realistic solutions to the complex problem of the border in Northern Ireland.”