The European Union’s chief Brexit negotiator warned U.K. Prime Minister Theresa May that substantial progress on the U.K.’s orderly withdrawal from the bloc is needed next month if there’s to be a deal.

“October will be the moment of truth,” Michel Barnier told reporters in Brussels. “It’s then we will see whether the agreement we’re hoping for will be within our grasp.”

Barnier was speaking on the eve of an EU summit in Salzburg, Austria, where leaders are expected to discuss holding a further meeting in November to sign off on a Brexit deal. Both sides admit they won’t hit their original deadline -- their gathering in mid-October -- but say time remains tight to allow approval by both the British and European parliaments.

EU officials say the U.K. will have to return to the negotiating table between the four-day Conservative Party conference in Birmingham that winds up Oct. 3 and the summit in Brussels less than three weeks later. They say the U.K. needs to compromise on the major obstacle to a deal -- how to keep an invisible Irish border after Brexit and there has barely been any progress on that since the start of the year.

“Our proposal for the backstop for Ireland and Northern Ireland has been on the table since February,” Barnier said. “We are ready to improve this proposal.”

Two Stages

As well as the Irish question, the two sides need to converge on an outline for future economic, trade and security cooperation. That will be the main topic of debate when the EU’s 27 other leaders meet without May over lunch in Salzburg on Thursday.

May wants to stay close to the EU for trade in goods but to go it alone on services. The EU says that won’t work because its single market is indivisible.

Brexit is being done in two stages: First the divorce deal, which will enable a 21-month transition phase when the U.K. leaves the EU in March 2019; then a full negotiation over future ties.

While the November deadline is now an open secret in Brussels, the EU wants to keep the pressure on the U.K. throughout October.

EU President Donald Tusk, who chairs summits, said in a statement Tuesday that leaders at Salzburg will discuss how to organize "the final phase of the Brexit talks, including the possibility of calling another European Council in November.”

Irish Foreign Minister Simon Coveney said he wanted to see the U.K. step up their engagement in negotiations over the border to achieve an agreement in October.

“Some people seem to be suggesting that we can just move past the leaders’ meeting in October and into November,” Coveney told reporters in Brussels after meeting Barnier. “That is not the view of Ireland. We want to see substantial progress.”