BRUSSELS (AP) " The European Union and Britain started a third round of Brexit negotiations on Monday with EU negotiator Michel Barnier testily berating the British government for what he perceives as a lack of focus and insufficient progress during the five months since it triggered divorce proceedings.
Refusing to bow to British requests to begin discussing a future relationship while it remains unclear how the two sides can split on good terms, Barnier insisted that the government of Prime Minister Theresa May must shake off its diplomatic sloth.
"To be honest, I am concerned," Barnier said during a brief welcome appearance with British counterpart David Davis.
"Time passes quickly," he said, adding he was "ready to intensify" the high-level negotiations that now consist of one four-day session a month.
Both sides are facing a March 2019 deadline to seal a deal to disentangle Britain from the EU and to broker the terms of their post-split relationship. The bulk of the negotiations need to wrap up in the fall of next year to allow for formal ratification by both sides.
"We must start negotiating seriously," Barnier said. "We need U.K. papers that are clear in order to have constructive negotiations. The sooner we remove the ambiguity, the sooner we will be in a position to discuss the future relationship and a transitional period."
Davis and Britain have been trying to nudge the EU toward discussing their divorce and future trade relations simultaneously. The EU has insisted that key issues of the withdrawal must be dealt with before any post-Brexit discussions can begin. Britain is hoping those discussions can start as soon as October.
"The week ahead is about driving forward the technical discussions across all the issues " all the issues," Davis said, turning to Barnier to underline his point.
The negotiators then disappeared into EU headquarters to discuss the issues that Barnier insists must take precedence. They range from the rights of European citizens living outside their native countries to the status of the Ireland-Northern Ireland border and the outstanding costs owed by Britain to the EU budget.
Tuesday will mark five months since May initiated the two-year divorce process and discussions since then, interrupted by a British general election as well as the summer, have yielded little progress.
On the EU side, the frustration is increasingly evident. Germany's main business lobby group, the Federation of German Industries, criticized the British government Monday for what it called an unclear stance on the future.
Dieter Kempf, who heads the influential group, said "appreciable progress can hardly be expected" during the four days of talks scheduled for this week. Kempf said the U.K. must make clear statements on the terms of its withdrawal, but that there doesn't appear to be a single agreed-upon British government position.
He added that British proposals on customs arrangements after the U.K. leaves the EU would require "disproportionately high bureaucratic effort" and are impractical for companies.
British Brexit minister Davis acknowledged that this week's talks will be mainly technical, but urged EU negotiators to show "flexibility and imagination."
"We want to lock in the points where we agree, unpick the areas where we disagree, and make further progress on a range of issues," he said Monday.
Britain has released a series of position papers in recent weeks on various aspects of Brexit, but they received a muted reception from Brussels.
Meanwhile, Britain's main opposition Labour Party announced Sunday that it backs the U.K. staying in the EU customs union and single market, which guarantees tariff-free trade, during a post-Brexit "transition period." The party argued such a period of several years would give much-needed certainty to businesses and consumers.
In return for remaining a member of the single market, Britain would have to agree to abide by the EU's four freedoms, including the freedom of movement within the bloc. And by remaining in the customs union, Britain would not be able to carve out its own trade deals, including one mentioned by May and U.S. President Donald Trump.
The government has also called for a transition period, but insists Britain will be out of the single market and customs union once Brexit actually takes place.
Geir Moulson contributed from Berlin. Lawless wrote from London.