The UK has put forward proposals to end the Brexit deadlock - but will not allow the European Union to keep hold of the written details for fear of leaks.
Brussels is becoming increasingly frustrated that no "concrete" suggestions to replace the controversial Irish backstop have been submitted.
But British sources insisted papers setting out Boris Johnson's position had been shown to the European Union side, even though they were taken back at the end of meetings.
It was "the nature of the Brussels system" that any documents shared with the EU would also be sent to the member states.
"Once you share it with 27 countries you are not in control of the document," a source said.
The European Commission again said the ball was in the UK's court to produce a formal written proposal following Mr Johnson's talks with Jean-Claude Juncker in Luxembourg on Monday.
"We are showing them papers," the Government source said. "The difference is we are not leaving them with them."
The UK side has produced a version of the Withdrawal Agreement with the backstop removed to show Brussels officials what changes Mr Johnson requires.
It has also shown the EU side some of the proposals to replace the backstop.
Commission president Mr Juncker and Mr Johnson met in Luxembourg on Monday - along with Brexit Secretary Stephen Barclay and Brussels' chief negotiator Michel Barnier.
They agreed to step up talks, with a mixture of technical and political talks between the two sides expected this week.
Daily meetings between the UK's officials, led by Mr Johnson's Europe adviser David Frost, and the EU's Taskforce 50 could begin next week.
European Commission spokeswoman Mina Andreeva told reporters in Strasbourg "we are available to meet anytime, any day, everyday if the UK wants to meet us".
She said "we are still waiting for concrete proposals from the UK side" and added "it's now the UK's responsibility to come forward with legally operational solutions that are compatible with the Withdrawal Agreement that are necessary in order to move the discussions forward".
The UK is expected to delay producing a formal submission until it can be sure the EU will not "trash it".
Nothing is expected before the UN General Assembly meeting in New York next week, where Mr Johnson is expected to have talks with European Council president Donald Tusk and German Chancellor Angela Merkel.
The proposals may not be produced until after the Conservative Party Conference, which finishes on October 2 - leaving a short window before the crunch European Council summit on October 17 where Mr Johnson hopes a deal can be struck.
Meanwhile, Cabinet minister Robert Buckland dismissed Luxembourg Prime Minister Xavier Bettel's attack over Brexit as an "unfortunate media stunt".
A podium set up for the UK's Prime Minister was left empty as Mr Bettel delivered an onslaught against Mr Johnson's handling of Brexit following their meeting in Luxembourg on Monday.
Asked whether Mr Johnson's shared the view that it was a "media stunt", the Prime Minister's official spokesman said: "I will leave it for others to reach their own judgment on what took place."
The spokesman pointed out that Mr Bettel had said he wanted a "good, friendly relationship with the UK going forward".
As judges at the Supreme Court considered whether Mr Johnson's decision to suspend Parliament for five weeks is lawful, the Justice Secretary refused to rule out a second temporary shutdown.
Asked whether it was remotely conceivable that Mr Johnson could suspend Parliament again, Mr Buckland told BBC Radio 4's Today programme: "Harold Wilson said a week is a long time in politics, it seems like an hour is a long time in politics at the moment, and for me to sit here and imagine what might happen at the end of October, I think is idle."
Campaigners against a no-deal Brexit are suspicious of the Government after Mr Johnson repeatedly stated the UK will leave the EU on October 31 with or without a deal despite a law requiring the Prime Minister to seek a delay rather than crash out without an agreement.
Shadow attorney general Baroness Chakrabarti raised concerns over how the Government will treat the legislation - known as the Benn Act - designed to stop it forcing through a no-deal Brexit on October 31.
She told Today: "Ministers in this Johnson government bizarre dystopian universe have now indicated that they might not even abide by the terms of that legislation.
"We've seen briefing from Number 10 that they might prorogue Parliament a second time to avoid the enforcement of the Benn legislation or the scrutiny of the House of Commons, and that they're thinking of other ways to avoid that legislation.
"This is how serious things have got in this country under a far-right, outright government."