European Union Chief Negotiator in charge of Brexit negotiations with Britain Michel Barnier | Thierry Charlier/AFP via Getty Images Brussels to UK: Give us clarity on divorce bill or Brexit talks will stall EU diplomats regard recent flurry of Brexit position papers from the UK as distraction tactic.

Britain must come forward with a proposal for how to calculate its EU exit bill or next week’s Brexit talks will come to a grinding halt, according to three senior diplomatic officials briefed on the negotiations.

At next week's round of talks, according to the three senior officials spoken to by POLITICO, Brussels expects U.K. Brexit Secretary David Davis to provide precise details on which obligations in the EU budget it is willing to pay for — in short, a methodology for calculating the bill. Although Davis has acknowledged that Britain has financial obligations to the EU, which need to be resolved as part of the withdrawal process, a methodology is something the U.K. has thus far pointedly refused to provide.

EU negotiators will also demand more detail on how the U.K. intends to permanently guarantee rights for EU citizens living in Britain (and vice versa) and specifications about Ireland's border.

The EU's chief Brexit negotiator Michel Barnier underlined Monday that talks on trade and other aspects of the U.K.'s future relationship with the bloc can only move forward once sufficient progress has been made on the separation issues.

"Looking forward to discussing these papers with UK. Essential to make progress on citizens rights, settling accounts and Ireland," Barnier said in a tweet, referring to nine official position papers that have come out of the EU since June.

In the two weeks running up to the talks, the U.K. government has been bombarding its EU counterparts with a series of position papers on everything from future customs arrangements to the handling of confidential documents.

But the majority of the proposals refer to the U.K.'s future relationship with the bloc, rather than the separation issues that the EU wants to tackle first. It regards the flurry of documents from the U.K. as a distraction tactic, designed to pressure its negotiators into talking about future trade.

"We feel they have come up with these papers to distract attention away from issues around the financial settlement," one of the diplomats said, suggesting that the documents served more as a smokescreen rather than an actual negotiating tool for this round of talks.

Another senior EU diplomat welcomed the fact London has begun clarifying its position, but underlined that the papers still lack detail. "The U.K. papers have strong words, but with no substance. They've not really given real answers," the official said.

If this round of talks remains deadlocked, it is hard to see how the negotiations can move forward fast enough for EU leaders at a European Council summit in Brussels in October to be satisfied that "sufficient progress" has been made on the three separation issues. If not, then the talks cannot move on to the U.K.'s future relationship with the bloc.

“This is not about numbers, but the Brits need to explain, on the one hand, that they have certain obligations but also what they are. Otherwise, the whole process becomes nonsensical,” said one of the diplomats who spoke on the condition of anonymity. “They need to move the ball at least ten yards down the field.”

The EU has already outlined a full list of bodies and funds covered by the financial settlement, which has been estimated at up to €100 billion.

That includes money for the European Court of Justice, the police agency Europol and capital that gets poured into the European Investment Bank. Other programs for which the EU wants funds from the U.K. include the European Regional Development Fund, which supports things like small and medium-sized enterprises and the low-carbon economy, and the Youth Employment Initiative.

If London fails to make a meaningful pledge, its wish to discuss a future trade relationship with the EU come October will be scuppered, the officials said.

“The first round [of negotiations] was for presentations, the second for common understanding — especially on the financial obligations — the third one [next week] will be crunch time and the fourth [in September] getting stuff done,” said an EU diplomat who is following the negotiations closely.

To grease the wheels during next week's talks, the EU is ready to grant Britain some flexibility on how it ensures EU citizens' rights.

Privately, officials in Brussels admit that while a deal on the financial settlement is politically difficult, it is technically easily implemented. Making progress on the matter of citizens' rights, on the other hand, is politically less contentious but technically arduous.

To grease the wheels during next week's talks, the EU is ready to grant Britain some flexibility on how it ensures EU citizens' rights. But in return, it will demand "a permanent guarantee" on matters such as pension rights for EU nationals residing in the U.K. after Brexit as well as family reunification.

"If the U.K. cooks up a system we would sit down and talk about it," one of the diplomatic officials said.

Ireland is expected to be the least contentious issue on the agenda because both sides share a strong desire to keep the peace process on track. But Brussels will demand more details on how to preserve the Common Travel Area between Northern Ireland and the Republic of Ireland as well as the Good Friday peace deal.

Under no circumstances will Barnier give in to pressure from Davis to discuss trade and customs issues, the officials said, even though the U.K. laid out its proposal on transitional and long-term customs arrangements with the EU last week.

For others, next week's talks are unlikely to achieve much. “I think that a final deal will be very hard on the financial settlement. Politically it is very hard as people will say 'why did you agree to that if not getting reassurances on other aspects.' In the end, it will have to be some kind of package deal,” said Pieter Cleppe, who heads the Brussels office of Open Europe, a British think tank.

The U.K.'s Department for Exiting the European Union declined to comment, but a government official had earlier told POLITICO: “We certainly are engaging on their arguments on financial matters, on a line by line basis. We’re just not writing them an alternative.”

Charlie Cooper contributed reporting.