Nigel Dodds said the Northern Irish party which props up Prime Minister Theresa May has agreed that the “UK stands together and nothing will happen that will cause the breakup of this great United Kingdom”.
The deputy leader launched an attack on Dublin accusing them of “disgraceful” behaviour.
He told MPs: “It should come as no surprise that the Dublin and Irish government wishes to advance its interests.
“The way it has gone about it in such an aggressive and anti-unionist way is disgraceful and has set back Anglo-Irish relations and damaged the relationships built up within Northern Ireland in terms of the devolution settlement – and that is going to take a long time to repair.
“The reality is that one of the good things that came out of yesterday is that from all sides of this House – Labour, Conservative, backbenchers, Ruth Davidson, Carwyn Jones, everybody – there is now an agreement that the United Kingdom stands together and nothing will happen that will cause the break-up of this great United Kingdom.”
“We will not allow any settlement to be agreed which causes the divergence politically or economically of Northern Ireland from the rest of the United Kingdom.”
Brexit minister David Davis threw his support behind Mr Dodds saying “you’re dead righ” and said the issue of a frictionless border between the UK and Ireland was best dealt with in the next phase of Brexit talks.
Speaking during a House of Commons debate, Mr Dodds accused Dublin on Tuesday of acting in a “reckless and dangerous” way, saying it was putting at risk years of good Anglo-Irish relations over Brexit.
He said: “The Irish Republic are flexing their muscles and using their current position to try to gain wins for them,” Dodds said, speaking in Westminster.
“I don’t argue with their desire to advance their interests but they’re doing so in a reckless and dangerous way which is putting at risk years of good Anglo-Irish relations and good cooperation within Northern Ireland.”
He said it would take “a long time to repair” the damaged relations between the north and south.
It came at the same time Mr Davis insisted it is “emphatically” not that the case that any part of the UK will remain in the customs union or the single market after Brexit talks broke down yesterday over the Irish border.
On a dramatic day in Brussels, Mrs May and Mr Juncker were involved in an extraordinary row over the future of the Irish border ahead of a crunch deadline next week.
Mrs May seemed on the verge of negotiating a deal which would move Brexit talks forward to trade before the DUP made a furious intervention.
DUP leader Arlene Foster refused to accept any terms which would see Northern Ireland leave the EU on different terms to the rest of the UK after Mrs May proposed aligning the state with the Republic.