Theresa May asked her greatest political enemy Jeremy Corbyn to help work out a joint plan for Brexit, in an attempt to break the deadlock and prevent the U.K. crashing out of the European Union without a deal.

The prime minister’s appeal to the opposition Labour Party leader opens the door to the possibility of a much softer form of Brexit, potentially keeping the U.K. inside the EU’s customs union. It would be a massive breach of May’s own negotiating red lines, but good news for business. The pound rose.

Corbyn welcomed May’s move and said he would be “very happy” to meet her.

After seven hours of talks with her Cabinet ministers, the premier said the U.K. will need an extra delay beyond next week’s potential cliff-edge deadline of April 12 to resolve the crisis.

“This debate, this division, cannot drag on much longer,” May said in a statement to television cameras at her 10 Downing Street office. “It requires national unity to deliver the national interest.”

The prime minister’s offer to Corbyn is another sign of the desperation and disarray that has overtaken her government as it struggles to complete Britain’s acrimonious separation from the EU. Parliament has rejected the deal she negotiated with the bloc three times, with Corbyn’s Labour consistently voting against it. She has tried cross-party talks before, but they led nowhere.

May’s plan has four parts:

  • Negotiations with Corbyn to agree a joint plan to ensure the U.K. leaves the EU with a deal. This will focus on the future relationship.
  • A May-Corbyn plan would be put to Parliament for approval, and the premier would then take it to the EU leaders’ summit on April 10 to be signed off.
  • If May and Corbyn can’t agree, they would put forward “a number of options for the future relationship” between the U.K. and the EU, for the House of Commons to vote on. The Government would promise to deliver whatever Parliament decides.
  • Legislation would then follow to allow the U.K. to leave the EU and avoid the need to take part in European Parliament elections next month.

May said her unpopular Withdrawal Agreement, which deals with the terms of the divorce, rather than the future partnership, will need to be passed as part of any arrangement with Corbyn.

In the past two weeks, rank-and-file politicians have taken control over the Parliamentary agenda in an attempt to solve the crisis themselves. But none of the Plan B options they’ve put forward has won a majority. In the most recent set of votes on Monday, a proposal to keep the U.K. in a customs union common tariff zone with the EU came closest, losing by just six votes.

“I’m very happy to meet the prime minister,” Corbyn said in response to May’s offer. “I don’t want to set any limits, one way or the other, ahead of those meetings. We recognize that she has made a move.”

Corbyn said he wants a customs union with the EU and continuing access to “vital” markets. “And we’ll ensure that those are on the table,” he said.

Membership of the EU customs union, with its single tariff regime and common trade policy, would destroy one of the main prizes of leaving the bloc for Brexit supporters: setting Britain free of European rules to be able to strike trade deals with other countries around the world.

May made leaving the customs union a red line during two years of talks with the EU. That might now have to change.