Sir Jeffrey Donaldson was reacting after the European Commission vice president, Maros Sefcovic, announced that the bloc would table “very far-reaching” proposals within the next fortnight.
Mr Sefcovic said he hoped those would form the basis of intensive discussions throughout the rest of October and November as the UK and EU try to resolve their differences over the trading arrangements that have created economic barriers between Northern Ireland and the rest of the UK.
“We were told weeks ago that the EU were not in a position where they were ever going to reopen negotiations, so I think we’ve breached the first wall and I think that is the result of unionists standing together and saying, ‘look, we cannot support this protocol, we cannot support an Irish Sea border’,” Mr Donalson said.
“I think that the pressure we have brought to bear and the steps that have been taken in the last few weeks have focused minds both in London and in Brussels, and I’m pleased that we’ve made this level of progress.
“We still have a long way to go, I don’t pretend otherwise, but I think at least now we’ve broken through. We’ve opened up the protocol and there is a beginning of a negotiation. We’ll see what emerges from that.”
Mr Donaldson has threatened to pull his ministers out of Stormont — a move that would collapse power-sharing in Northern Ireland — if major changes to the protocol are not secured in the coming weeks.
He said he had been assured by British prime minister, Boris Johnson, and the UK’s Brexit negotiator, Lord Frost, that if the EU does not “step up to the mark” with significant reforms, then the government will move unilaterally to “restore Northern Ireland’s position within the UK internal market”.
“The EU will bring forward their proposals, I’ve no doubt that those proposals will fall short of what the UK need and certainly what we need, and there will then follow a period of what Lord Frost called ‘intensive negotiations’,” he told BBC Radio Ulster.
The DUP leader added: “I’ve certainly seen a change in the tone and language being used by the EU, which is welcome.”
Asked whether his call for a renegotiation was at odds with the EU insistence that it was not renegotiating the protocol, rather offering mitigations and flexibilities, Sir Jeffrey said: “The EU can call it what they will, they can present it in whatever way they wish, but, in the end, the wall has been breached, we’ve opened up the protocol.”
He said he hoped talks between the UK and EU would be “meaningful”.
Mr Donaldson said “practical measures” could be found that would differentiate between goods whose end destination was Northern Ireland and those at risk of crossing the Irish border into the EU single market — with Irish Sea checks only required on the latter.
He said he would support “proportionate” processes that would enable the EU to protect its single market.
The DUP leader also said the standoff over whether the European Court of Justice should be allowed to arbitrate on trade disputes related to the protocol rules was an “important issue” and said he believed the UK would push for a more “independent” arbitration mechanism.
Mr Donaldson added: “I hope that the EU will step up and recognise that Northern Ireland’s place within the UK internal market needs to be respected, but if they don’t, then I expect that the UK government will take the necessary steps to do that and ensure that our place within the UK internal market is restored.”