LONDON (AP) — The U.K. and the European Union were poised Monday to end years of wrangling and seal a deal to resolve their thorny post-Brexit trade dispute over Northern Ireland.

Striking an agreement at a meeting with European Commission President Ursula von der Leyen would be a victory for Prime Minister Rishi Sunak — but not the end of his troubles. Selling the deal to his own Conservative Party and its Northern Ireland allies may be a tougher struggle.

Sign of a potential U.K.-EU breakthrough came Sunday, when the two sides announced that von der Leyen will travel to England for a meeting with Sunak in Windsor, about 20 miles (32 kilometers) west of London. A joint news conference is penciled in, followed by a statement by Sunak to the House of Commons.

If all goes to plan, it could end a dispute that has soured U.K.-EU relations, sparked the collapse of the Belfast-based regional government and shaken Northern Ireland’s decades-old peace process.

Northern Ireland is the only part of the U.K. that shares a border with an EU member, the Republic of Ireland. When the U.K. left the bloc in 2020, the two sides agreed to keep the Irish border free of customs posts and other checks because an open border is a key pillar of Northern Ireland’s peace process.

Instead there are checks on some goods entering Northern Ireland from the rest of the U.K. That angered British unionist politicians in Belfast, who say the new trade border in the Irish Sea undermines Northern Ireland’s place in the United Kingdom.

The Democratic Unionist Party collapsed Northern Ireland’s Protestant-Catholic power-sharing government a year ago in protest and has refused to return until the rules are scrapped or substantially rewritten.

The DUP has stayed largely silent in recent days, saying it needs to see the details of a deal before deciding whether it meets the party’s self-imposed tests.

Hints of compromise towards the EU also have sparked opposition from hard-line euroskeptics who form a powerful bloc in Sunak’s governing Conservative Party. Critics include former Prime Minister Boris Johnson, who as leader at the time of Brexit signed off on the trade rules that he now derides. Johnson was ousted by the Conservatives last year over ethics scandals, but is widely believed to hope for a comeback.

Jacob Rees-Mogg, a prominent pro-Brexit Tory lawmaker, said acceptance of any deal “will all depend on the DUP. If the DUP are against it, I think there will be quite a significant number of Conservatives who are unhappy.”

Sunak has said Parliament will get to debate any deal he strikes, but he hasn’t promised lawmakers a binding vote on it.