DUBLIN: The leader of Northern Ireland's highly influential Democratic Unionist Party on Tuesday warned British Prime Minister Theresa May against any Brexit compromise with Brussels that could increase checks on trade between the province and the rest of Britain.
The DUP are key allies for May, providing her Conservative government with a slim parliamentary majority after the Tories lost their overall majority in the 2017 general election.
"We cannot have either a customs border down the Irish Sea or a regulatory border, because that would make us separate from the rest of the United Kingdom", DUP chief Arlene Foster said in an interview with Bloomberg.
"That doesn't work from a constitutional perspective and that doesn't work from an economic perspective either."
The European Union has proposed that Northern Ireland be allowed to remain in Europe's single market for goods in order to keep the border with the Republic of Ireland open.
London has countered that this would breach the integrity of the United Kingdom.
Earlier on Tuesday, May said on BBC radio that a new proposal would soon be put to the EU, which would preserve trade between Northern Ireland and mainland Britain whilst also satisfying the requirement for some form of checks.
"We believe that there is a way that this can be done which does preserve our integrity -- that's the proposal that we're working the details on," May said in an interview, adding that the plan would be revealed "in due course".
After a bruising summit in Salzburg, during which her Brexit proposal was roundly rejected by EU leaders, there have been reports that May's latest plan offers a compromise by allowing for some form of regulatory checks in the Irish Sea in exchange for avoiding a customs border.
A hard border in Ireland is forbidden under the 1998 Good Friday Agreement, which brokered peace in the region after decades of border clashes between nationalists, unionists and British troops.
However in a separate interview published Tuesday, Foster claimed the terms of the accord -- also known as The Belfast Agreement -- could be altered to shape Northern Ireland's relationship with the EU.
"It has been deeply frustrating to hear people who voted 'Remain' (in the EU) and in Europe talk about Northern Ireland as though we can't touch the Belfast Agreement. Things evolve, even in the EU context," she said in an interview with The Daily Telegraph.
"There has been a lot of misinterpretation, holding it up as a sacrosanct piece of legislation."
Mary Lou McDonald, leader of the all-Ireland nationalist party Sinn Fein, said the comments "reveal a reckless disregard for the peace process, prosperity and progress".