Britain’s Rishi Sunak took a chance when he agreed to undertake discussions in secret about post-Brexit trade regulations for Northern Ireland, providing little information beyond assurances to two political factions that have a reputation for making life difficult for prime leaders.

After ties with the European Union reached a breaking point under his predecessors Boris Johnson and Liz Truss, who adopted a hard line and were accused of damaging discussions by talking in public, Sunak saw secrecy as essential to rebuilding confidence with the EU.

But it was secrecy that fostered suspicion among two big hitters in the years-long Brexit debate – the Democratic Unionist Party (DUP), Northern Ireland’s biggest unionist party, and the pro-Brexit Conservative European Research Group (ERG).

With both groups saying they will now consider the detail of Monday’s deal before offering a verdict, Sunak will hope the changes he has negotiated will overcome the sourness that has coloured the weeks-long build up to what he called a decisive breakthrough with the presentation of the “Windsor Framework”.

“I am pleased to report that we have now made a decisive breakthrough, together we have changed the original protocol and are today announcing the new Windsor framework,” Sunak told a news conference.

He said the deal would ease trade between Britain and Northern Ireland, firmly root the province’s place in the United Kingdom and give lawmakers there a say in whether they must implement EU law, with London having a veto.

“I believe that today’s framework addresses them (Northern Ireland’s concerns) … I believe that what we have achieved today is a real breakthrough.”

The European Commission’s president, Ursula von der Leyen, described the deal as an historic one which opened a “new chapter” in relations with Britain, praising “dear Rishi’s” honesty in his dealings with the bloc.