LONDON — Get ready for the Brexit Big Bang.

After more than a year of excruciating negotiations, and despite continuing fierce differences, the U.K. and the EU have reached a shared understanding of how they can clinch a deal.

It will be hard, fast and with a bang, at a yet-to-be-arranged special summit in Brussels in November, according to senior government officials and diplomats in Brussels, the U.K. and other EU capitals.

There is still no guarantee of success, particularly given the continuing sharp divide over how to solve the Irish border issue, and the timetable could yet slip further. But if a deal is clinched, according to the diplomats and officials in Britain, Brussels and Berlin, it will come at a highly scripted moment to be quickly followed by EU27 leaders approving the package.

Both sides hope it will be a “transformative” political moment for Theresa May, with the goal of a jolt of momentum that will help the U.K. prime minister force a deal through parliament before her opponents can pick it apart.

Negotiators in London and Brussels are now working hand-in-glove to get the deal over the line, intent on avoiding any drip-drip of mini developments that critics can gnaw on.

A bland statement issued by Brexit Secretary Dominic Raab following an “extended phone call” Friday morning with his opposite number Michel Barnier was typical of this tight-to-the-chest approach. “Our teams are closing in on workable solutions to the outstanding issues,” said Raab with no hint of what they might be.

Barnier, the EU’s chief negotiator, offered his own bland confirmation, noting differences but stressing “useful dialogue,” “progress” and “continuing our discussions to find common ground on the future relationship.”

A week earlier, the pair had met in Brussels, but chose not to release any statement at all, or hold a press conference.

Chequers model

May’s tactics in strong-arming her ministers into supporting her Brexit plan in July may serve as a useful pointer to the overall Brexit endgame. She unveiled the full proposal to ministers shortly before a Cabinet retreat at her Chequers country residence. And while some big hitters, including David Davis and Boris Johnson, resigned in protest, May succeeded in making a forceful case that she alone has the best way forward.

In November, she will make a similar case, according to a senior U.K. official: her best hard-fought deal or the cliff edge.

Timing will also be critical. EU officials are concerned that anything agreed before the Conservative Party conference in early October could spark an angry Brexiteer backlash. And EU diplomats, speaking on condition of anonymity, said Barnier has told them to “avoid rocking the boat” before then too.

With the withdrawal treaty now 80 percent to 95 percent complete — depending on which official you ask and his or her mood at the moment — the last push will focus on the “political declaration,” a document setting forth the framework of the future relationship that will accompany the withdrawal treaty. There is now a growing consensus in Brussels and London about what it will look like.

According to three leading EU27 officials and diplomats working on Brexit, the final compromise will reflect some aspects of May’s Chequers plan while also remaining sufficiently vague to keep all sides happy.

One EU diplomat said: “The more generic it will be, the easier it will be for May to keep together the different souls of the Tories.”

Keep it too vague though, and MPs on either side of the debate, as well as MEPs who also have a vote, have said they will reject it as a leap of faith. That position was echoed by French Europe Minister Nathalie Loiseau, who last week said France is against what she called a “blindfold Brexit.”

The equation is a bit easier in Brussels, where officials maintain that the political declaration cannot legally bind the EU27 to specific terms of a future trade accord.

To avoid the vagueness charge, one proposal that has been floated is to make the final document a combination of “high-level aspiration” in some core areas and “incredibly detailed agreement” in others, according to a senior U.K. official.

Such a structure would give some cover from attacks on the U.K. government that it is giving up its financial leverage, as Brexiteers see it, in exchange for only vague promises of a future trade arrangement.

This concern is reflected in one major outstanding area of disagreement on the future relationship: how the U.K. can ensure the EU sticks to its word after Brexit.

At an August 22 meeting between Barnier and Raab, the U.K. Brexit secretary called for a legal guarantee on the future framework to be inserted into the Withdrawal Agreement, according to an EU Brexit official familiar with the conversation. “Not only on the process, but also on the outcomes,” according to one familiar with the conversation.

This, the official said, is “not possible.”

A second idea is for “review clauses” to be inserted into the political declaration, which will allow both sides to argue that potential problems with the agreement can be ironed out at a later date.

One high-level official said these clauses should not give the impression of “perpetual divorce,” but could help allay concerns in the EU that the U.K. might emerge with “competitive advantages.” The prospect of a formal mechanism to review the arrangement could also help persuade Brexiteer MPs that the Northern Ireland border solution could be revisited in the future.

Both sides have already agreed on the need for a future “political joint committee” staffed with officials from both sides, sitting under a joint ministerial committee that will meet regularly to help resolve disagreements.

A separate independent arbitration mechanism — the details of which are still to be worked out — will sit alongside the committees.

Next steps

November is now being eyed as the time to bring together these potential ingredients. Senior EU officials in the Commission and in the Council now expect a deal on the withdrawal agreement to be clinched in one last marathon negotiation — potentially an all-nighter — that month, with May playing a direct personal role in the most critical endgame bargaining.

But there are many steps to choreograph first.

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On Thursday, Barnier will brief EU leaders over lunch at an informal summit in Salzburg, Austria, and they will discuss the political declaration for the first time in detail. Based on that conversation, the negotiator will then begin drafting the text — two diplomats said he has not begun doing so yet.

Crucially, the leaders will not alter or add to Barnier’s negotiating mandate — both because no official action is to be taken in Salzburg, but also because EU leaders remain highly confident their carefully scripted approach to the talks has worked well so far.

EU officials said that hashing out a withdrawal agreement will require reassuring language on the Northern Ireland border that will ensure Dublin feels its interested are protected, but at the same time leaves some crucial details to be sorted out during the 21-month post-Brexit transition period.

One EU diplomat said that will require at least some concession from May on the Irish border. London has rejected the EU’s “backstop” insurance plan that is designed to avoid the need for a hard border on the island by requiring Northern Ireland to remain inside the EU’s customs union while excluding the rest of the U.K.

“They want to deal with this as part of the future relationship,” the diplomat said. “But you can’t be sure that the future relationship stuff will work out. For us, it’s a matter of trust.”

Once a deal is hatched, the EU will leave it to May to steer the agreement through the U.K. parliament. At that point, Brussels can only sit back and watch. If May succeeds, there’s a deal. If she fails, several officials in Brussels said they expect complete political turmoil, potentially including a general election or even a new referendum on EU membership.

What no one in Europe believes though is that the U.K. is seriously contemplating leaving without a deal.

Out of 14 diplomats approached by POLITICO not one said they thought the U.K. is serious about going ahead with no deal. “[The Brits] will keep on publishing material on it, no doubt, but it’s really difficult to believe in it,” one said.

Matthew Karnitschnig and James Randerson contributed reporting.