Brexit talks could go into their crucial "tunnel" phase as early as Monday, officials believe – in latest sign a trade deal is moving within reach.
Michel Barnier and his team arrived in London on Thursday evening by train and have been locked in intensive talks with their UK counterparts since Friday.
Negotiators are aiming to strike a last-minute free trade agreement to avoid a no-deal Brexit that would inflict tariffs on goods and chaos at ports when Britain leaves the single market at the end of the year.
In an early sign that both sides are now taking proceedings seriously, the two teams have informally agreed to stand down their media operations over the weekend's discussions.
The tentative information blackout is intended to give teams a space to talk earnestly and work through issues without posturing for the benefit of those outside the room. Just two weeks of negotiating time remain before it would become impossible to get a deal in place and ratified by the end of the year.
If discussions over the weekend are judged to have gone well, things could be taken a step further, with a formal "tunnel" declared early next week, The Independent understands.
During the tunnel phase of talks, a small core of negotiators would work in total secrecy to hammer out of a deal without fear of interference from the outside.
"They're negotiating intensively over the weekend. Let's see after that," one EU official said of the tunnel phase.
The negotiating model, which delivered the withdrawal agreement last year, is seen in Brussels as crucial to finalising an agreement.
During that phase, documents are left unpublished, press reaction or comment is put off-limits, and even EU27 ambassadors are not kept informed of progress, for fear of leaks.
The UK government was coaxed back to the negotiating table on Wednesday after repeated overtures by telephone from Mr Barnier, who had to quickly patch-up relations between the two sides after an unhelpful EU summit.
Meeting in Brussels last week EU leaders had enraged Boris Johnson by saying it was up to him to make any concessions that would close the gap between the two sides.
UK sources say Mr Barnier gave the British team what they wanted in terms of assurances about how talks would be conducted – after Boris Johnson demanded a "fundamental change" in the bloc's approach to negotiations and temporarily walked out. Mr Barnier had originally been told by Downing Street there was "no point" in him coming to London.
The EU's chief negotiator is understood to be sanguine about most of the remaining issues in talks, with governance and a level-playing field on state aid seen as eminently solvable.
One clue as to how the state aid issue could be fixed comes from an unlikely source: the recently published UK-Japan free trade agreement.
In this deal, the UK has agreed to maintain and "operationally" independent competition authority", which Britain had previously resisting committing to in talks with the EU. EU officials have acknowledged slight UK movements on the issue in recent weeks that may come out over the weekend.
But it is the issue of fishing that is likely to prove the biggest stumbling block and could yet sink negotiations. EU diplomats say Michel Barnier isn't "worried about anything else but fish”.
In an update to MPs on Friday UK fisheries minister Victoria Prentish said the issue was "proving a difficult negotiation and the UK and EU positions are very far apart".
Despite accounting for a tiny proportion of the economy in the UK and most member states, the issue remains politically explosive on both sides of the Channel.
Industry insiders in France say the nation is preparing its fishing sector for a smaller catch after Brexit in a sign that President Emmanuel Macron is laying the ground for a delicate compromise in EU-UK talks.
Mr Macron has previously said France would not accept any Brexit pact that “sacrifices our fishermen”., and rejected London’s demand for annual negotiations on fish quotas in British waters, saying it damages EU industry.
However the French president said after last week’s summit of EU national leaders dedicated to Brexit that the French industry will no longer be in the same situation as today after year-end. Privately, his government has reportedly gone further, bluntly telling France’s politically influential fishing industry to brace for impact.
The UK says it wants a larger share of the fish in the sea than it currently enjoys under the Commons fisheries policy, and most observers of the industry agree that the UK has historically had a raw deal.
But any sudden withdrawal of fishing rights for French fleets would also have a disastrous impact on the country's coastal communities. Mr Macron has yet to hint at a climbdown, at least in public – telling reporters at last week's summit that would not accept any Brexit deal that “sacrifices our fishermen”.
French Europe minister Clement Beaune reiterated the tough message going into the weekend, telling French television: “We thought the end of October was the final deadline. We are giving ourselves a few more days to give the negotiations a chance, but we need to know quickly."
He added: “If the British thought they could live with the ‘freedom’ of no deal outside the EU, if it was so easy and so comfortable, they would have already left without a deal."
A Number 10 spokesman told a Westminster briefing at the end of the working week that intensive talks "are continuing and they will continue over the weekend", with the round ending later on Sunday.
The EU has offered a further round of talks to be held in Brussels the following week, where the tunnel negotiations would be expected to take place if no further derailment occurs.
Additional reporting by agencies