The U.K. and the European Union are working against the clock to reach a compromise on what the Irish border should look like after Brexit as intractable sticking points remain just four days before a crunch meeting.

Talks between Ireland, the U.K. government and the Northern Irish party that props up May’s government in London are at a critical point, Irish Agriculture Minister Michael Creed said. He called for more detail from the U.K. on its proposal to avoid a hard border after Brexit.

“It’s squeaky bum time,” he said in an interview with broadcaster RTE, using a football-match analogy for the final stages of a game.

Prime Minister Theresa May needs to find a way of wording a commitment to the EU that Brexit won’t mean a hard barrier goes up between Northern Ireland and the Republic of Ireland when the 300-mile line dividing them becomes the U.K.’s new frontier with the EU. The issue is the main obstacle to Brexit talks moving on after an outline deal on the financial settlement was reached.

Reiterating commitments to the Good Friday Agreement that brought peace to Ireland after decades of violence could be part of the solution, according to four European officials. But Ireland is insisting on a written commitment that goes further, and makes sure regulations on each side of the border won’t diverge significantly after Brexit, one of the officials said. The pound continued to strengthen on Thursday on hopes of a breakthrough in divorce talks, which have shown little progress for months. The Times of London reported that an agreement on the Irish border is close, and the EU will offer a deal on the transitional arrangements that businesses are clamoring for as soon as January.

Speaking in private, one European official said the deal hadn’t yet been reached, and he put the chances of an agreement by next week at 60-40. Another European official saw a 50-50 chance.

The Times reported that the solution could hinge on giving Northern Ireland more powers locally over customs, energy and agriculture as a way to keep rules the same on each side of the border after Brexit. The U.K. proposal commits it to working to avoid regulatory divergence on the island of Ireland, the paper said.

That probably wouldn’t go far enough, according to a European official, familiar with Irish thinking. DUP lawmaker Ian Paisley, who rejects any agreement that would separate Northern Ireland from mainland Britain, said on Thursday that Brexit will mean Northern Ireland gets different rules to the Republic on matters such as agriculture.

“There’s areas where frankly divergence will come about because we in Northern Ireland, being part of the United Kingdom, believe we’re going in a different direction, for example on agriculture,” DUP lawmaker Ian Paisley said in an RTE interview on Thursday. “Why would we hold to certain policies that would hold us back.”

That could be a major obstacle. For now, farm animals roam freely across the border, which is all but invisible thanks to the EU, its single market, and its common agricultural policy. Brexit will mean a border probably has to go up somewhere as the U.K. plans to leave Europe’s single market and customs union. The U.K. also wants to strike trade deals with other countries: if U.S. food imports start coming freely into Northern Ireland then a border will be need to block them crossing the Irish border into the EU.

Ireland wants no border at all—for historic, political and economic reasons—and the EU has adopted the same stance. But no border means keeping Northern Ireland aligned with the regulations that apply in the Republic, and that could mean erecting barriers between Northern Ireland and mainland Britain. The DUP considers that a red line and their view is more important than ever as their lawmakers prop up May’s government in London.

On Monday, May has lunch with European Commission President Jean-Claude Juncker and is expected to present the formal offer on the divorce bill and Ireland. Brexit Secretary David Davis and his counterpart Michel Barnier may meet beforehand and the aim is to get a joint statement on progress. If all goes well, the EU would make clear that trade and transition talks can start, leaving everything stitched up in time for the Dec. 14 summit.

Businesses are desperate for negotiations to start on the transition deal that Britain wants to put in place after Brexit and also for talks to get going on trade—where the real battle will begin.