British Prime Minister Sunak and European Commission President von der Leyen agreed a deal on trade rules for Northern Ireland on Monday. Sunak said it would pave the way for a new chapter in Britain’s relations with the bloc. Sunak said during a press conference with von der Leyen that the two sides had agreed to remove “any sense of a border” between Britain and its province, a situation that had angered politicians on both sides. The announcement has won plaudits from business groups, who welcomed the easing of trade rules, and an EU promise that it would be willing to allow British scientists to join its vast research programme if Sunak’s Conservative Party accepts the deal.

Sunak has been looking to secure improved relations with the EU and the United States just four months into the office, without rattling his party’s pro-Brexit wing.

The deal seeks to resolve the tensions caused by the Norther Ireland protocol, a complex agreement which set the trading rules for the British-ruled region that London agreed before it left the EU but now says are unworkable.

Its success largely depends on whether it convinces Northern Ireland’s Democratic Unionist Party (DUP) to end its boycott of Northern Ireland’s power-sharing arrangements. These were central to the 1998 peace deal known as the Good Friday Agreement which mostly ended three decades of sectarian and political violence in Northern Ireland.

“I’m pleased to report that we have now made a decisive breakthrough,” Sunak said of his new “Windsor Framework”. “This is the beginning of a new chapter in our relationship.”

The issue of Northern Ireland has been one of the most contentious related to the Brexit. A return to a hard border between the province and Ireland, an EU member, could have jeopardized the 1998 peace deal.

But it remains to be seen whether the new terms will go far enough to end the political deadlock in Northern Ireland, where perceptions that the protocol loosened ties with Britain have angered many unionist communities.

Von der Leyen said she hoped the brake could be avoided if the two sides consulted each other extensively when introducing new laws and regulatory changes.

DUP leader Donaldson said “significant progress” had been made but they would not be rushed into a decision.

If the deal is accepted, the new changes would be phased in over the next few years. A parliamentary vote will take place once all parties have had time to study it.

Sunak aims to strengthen his leadership in the Conservative Party with a deal and move past the thorniest issue on his agenda as he seeks to catch up with the opposition Labour Party, now well ahead in opinion polls, before a national election expected in 2024.

If he fails, he will likely to face a rebellion from the eurosceptic wing of his party, reviving the deep ideological divisions that have at times paralyzed the government since the vote to leave the EU in 2016.

Sunak could have left the stand-off unresolved, but officials in London and Belfast say he has been motivated to act ahead of the 25-year anniversary of the Good Friday Agreement.

Sunak is hoping that a successful outcome will improve cooperation with the EU in areas beyond Northern Ireland, including the regulation of financial services and in helping to stem an influx of migrants in small boats across the Channel.