There are still too many questions and too few answers in talks between the European Union and Britain over the country's withdrawal from the bloc, EU chief negotiator Michel Barnier said on Friday.
Barnier also said the two should "de-dramatise" a backstop proposed by Brussels to avoid erecting a border on the island of Ireland after Brexit that would see the EU governing some of Northern Ireland trade.
"We are not asking for any new borders between Northern Ireland and the rest of the United Kingdom," Barnier said. "We must all de-dramatise this backstop... Ultimately these are only technical controls on goods, no more, no less."
The sensitive issue of the Irish border is a key conundrum in the Brexit talks.
Barnier was speaking as British Prime Minister Theresa May sought to convince her divided government to her plan for Britain's future after it leaves the EU next March and a status-quo transition period runs out at the end of 2020.
"We need a cast-iron guarantee in the withdrawal agreement to avoid a hard border, whatever the result of negotiations on the future relationship between the UK and the EU," he said.
He said some veterinary and phytosanitary checks were already being carried out between Northern Ireland and the rest of the UK.
Barnier reiterated that much remained to be done to reach a broad Brexit deal in October, leaving enough time for the EU's elaborate ratification process before the Brexit date in March.
"In the Brexit negotiations, there are still too many questions and too few answers," Barnier said. "Time is short. We need to have quickly realistic and workable solutions."
Barnier said outstanding issues included data protection, cooperation between police and judicial authorities and how to settle legal disputes that may arise under the withdrawal deal.
"LOSE-LOSE GAME"
May's plan for a "facilitated customs arrangement" would see Britain closely mirror EU rules and use technology to determine where goods will go and therefore which tariffs should apply.
Barnier said he would only comment once the proposal was fully unveiled, but suggested it may fall short: "Some of these checks can be implemented by technical measures but not all."
Barnier said the agreement on post-Brexit ties with Britain must ensure London would not be able to offer goods at a lower price should it decide to skip some EU standards.
"If we don't find a way with the UK to prevent this kind of dumping, the risk is we'll face huge difficulties in the next stage, when we will have to get agreement in 27 national parliaments, and even regional parliaments in some cases," he said, referring to the need for ratification by EU states.
He said Brexit was a "lose-lose game". Without a deal in place next March, Britain would risk crashing out with little idea of what new rules govern its ties with the EU.
With progress slow, some EU diplomats expect tense 11th-hour talks at the turn of the year, which may still prove insufficient.
"It seems more and more that Britain will have to ask for an extension of the two-year period for Brexit negotiations," said one EU diplomat involved in the talks.