Home Secretary Amber Rudd has dismissed a leak of difficult Brexit talks as "tittle-tattle" amid further reports of concerns in Brussels.
Ms Rudd also said it was a mistake that details of a dinner at Downing Street last week had appeared in the press, with the Government saying it would not enter into a briefing war with the European Union.
European Commission president Jean-Claude Juncker claimed that some in the UK "underestimate" the difficulties of Brexit, with Brussels indicating that the sequence of the talks and the complexity of the issues around citizens' rights are among the stumbling blocks.
Senior EU sources told the BBC that the UK failed to understand how the bloc works, prompting fresh fears Britain would fail to secure a trade deal after Brexit.
Prime Minister Theresa May has come under fire following reports Mr Juncker walked out of talks last week in Downing Street saying he was "10 times more sceptical than before".
Ms Rudd told ITV's Good Morning Britain: "We are not going to comment on leaks like this - they may or may not be true, elements of it - but the fact is there is going to be nearly two years of this type of negotiation going on and I think it would be a mistake for the Government to leap on and back on any sort of tittle-tattle that comes out."
The Government position is that "we can be relied on to keep gossip out of the press" so it can get a good deal for the UK, she added.
The Home Secretary, who was not at the dinner last week, told the Today programme on BBC Radio 4: "I'm not surprised that there is briefing coming out from different sides of a negotiation.
"But what we will always do is make sure that we conduct our negotiations more discreetly, shall we say, so that really we can have a freer negotiating hand.
"I think it's a mistake to allow those sort of details, if they are true, to come out from a dinner."
Mrs May has dismissed claims she is at loggerheads with Mr Juncker over her Brexit negotiating strategy as just "Brussels gossip".
European Commission spokesman Margaritis Schinas said he would not comment on leaks, but pointed out that Mr Juncker had publicly described the dinner as "constructive".
Asked if the dinner had been a "disaster", Mr Schinas said Mr Juncker had described it on Saturday as "a very constructive meeting in a friendly atmosphere" but "I have the impression sometimes that our British friends - not all of them - do underestimate the technical difficulties we have to face".
Mr Schinas added: "You can use this assessment and make your judgment on how you can characterise our understanding of the dinner."
Asked what "technical difficulties" Mr Juncker meant, the spokesman said there were "many things", including "the sequencing of the negotiation, the degree of difficulty involved in various stages".
On citizens' rights there were "25 different sub-topics that altogether form something that is just a part of the negotiation", Mr Schinas said.
"There are issues that clearly are not understood the same way, from a technical point of view. But we will work it out - it is in the commission DNA to work for solutions."
Speaking during a campaign visit to Lewes in East Sussex, Liberal Democrat leader Tim Farron said: "Whether you see these as leaks or Brussels gossip, the whirlwind of news following the May-Juncker meeting is a taste of what's to come.
"The reports show a Prime Minister who is complacent and seems to have no idea how difficult these negotiations will be."
Green Party co-leader Caroline Lucas, speaking at a campaign event in east London, told the Press Association: "I think these leaks over the weekend confirmed our worst fears really - that Theresa May is going into these negotiations utterly unprepared, completely arrogant and not understanding how the EU works.
"It's not surprising she's then putting the backs up of the 27 other member state governments, with whom she needs to keep on good terms if we're to try to get the best possible deal for the country."