European Council president Donald Tusk has delivered a scathing assessment of the UK's Brexit position less than 24 hours after Theresa May appeared to have secured an agreement among her divided Cabinet.
In comments which appear to make no attempt at diplomacy, Mr Tusk said the Prime Minister's Brexit plan "is based on pure illusion".
"I am glad that the UK seems to be moving towards more detailed position, however if media reports are correct then I am afraid the UK position is based on pure illusion." he said.
Speaking at a news conference alongside European Commission president Jean-Claude Juncker in Brussels, Mr Tusk added: "It looks like the [have your] 'cake' [and eat it] philosophy is still alive.
"From the very start it has been a key principle of the EU27 that there can be no cherry-picking and no single market à la carte.
"This will continue to be a key principle, I have no doubt."
Mr Tusk's blunt assessment follows the emergence of optimism from the UK Cabinet after their away-day at Chequers on Thursday.
Senior ministers suggested agreement had been reached – following their marathon talks at the Prime Minister's country retreat – on the UK's desired outcome for Brexit; which would see close future alignment to EU regulations in some areas, but no alignment in others.
Irish PM @campaignforleo says it’s ‘not possible for UK to be aligned to EU when it suits & not when it doesn’t. The UK needs to square that circle. It’s not yet squared. UK position
needs to be backed up with real detail. We are well beyond aspirations we need detail’ @SkyNewspic.twitter.com/wb4UBrxVop
— Mark Stone (@Stone_SkyNews) February 23, 2018
Earlier, the Irish Prime Minister called on the UK Government to provide "real detail" in its Brexit position, as he arrived at a summit of EU leaders in the Belgian capital.
"I think we are well beyond the point of aspirations and principles. We need detail," Leo Varadkar said.
"Hopefully when the Prime Minister speaks next week the UK will be more clear about what it wants in terms of the new relationship and will back that up with real detail; detail that can be written into a legal treaty with the EU."
Speaking to Sky News on their arrival at the summit in Brussels, a number of other EU leaders echoed Mr Varadkar's call, adding that they did not know the conclusions Mrs May and her Brexit "war Cabinet" had come to at their Chequers meeting.
"I am commenting on the outcome of the Chequers meeting when I know what the exact conclusions are," Mr Juncker said.
Asked when he expected to get detail on the British Cabinet meeting, Mr Juncker added, jokingly: "I am not the British Prime Minister. It would be good for Britain if I was!"
"You have to report to me what they did [at Chequers], that's your job!" Dutch Prime Minister Mark Rutte said.
Questioned about whether the EU side was maintaining its united line on Brexit and not allowing the UK to cherry-pick aspects of the EU, Mr Rutte insisted there was full agreement.
He said: "Yes we are aligned as 27 and yes we have very close ties with Britain.
"That's why, as good friends, we can bring the difficult messages like I did last Wednesday in Downing Street: asking Theresa May to be as clear as possible on what she wants to achieve.
Dutch PM @MinPres speak to @SkyNews as he arrives at EU summit. He says he doesn’t know what was decided at Chequers yesterday. “That’s your task – you have to report to me what they did!” But he says there remains complete unity among 27 remaining countries on #Brexitpic.twitter.com/mfohfxuZKb
— Mark Stone (@Stone_SkyNews) February 23, 2018
"I really believe that as 27 we have a reasonable position, that we want to stay as closely associated with the UK as possible but for example, membership of the internal market means serious obligations, membership of the customs union means serious obligations.
"So it's always, if you want something, there are certain rules you have to abide by."
Meanwhile, Mr Varadkar added: "It's not a la carte. It's not possible to be aligned with the European Union when it suits and not when it doesn't. That's not possible and I think the UK really needs to square that circle and it doesn't appear to me that that circle has yet been squared."
But in language that will be seen as encouraging by the British Government, the president of the European Parliament, Antonio Tajani repeated a phrase often used by Mrs May.
"The UK will be outside the European Union but not outside Europe," he said.
"We are working all together for a good Brexit. For us its important to achieve good solutions."
Mr Tajani's views could be increasingly important. He has been named as a possible candidate for Italian Prime Minister if a coalition led by Silvio Berlusconi's Forza Italia party tops the polls in next weekend's Italian election.
Last night, as UK ministers wrapped up their crunch Brexit talks at Chequers, the leaders of 13 EU countries were sitting down for dinner at a chateau on the edge of Brussels.
The informal dinner was hosted by the Belgian Prime Minister Charles Michel and among the guests were the EU's two most powerful leaders, French President Emmanuel Macron and German Chancellor Angela Merkel.
Among the others in attendance were the leaders of The Netherlands, Spain, Portugal, Italy, Bulgaria and Ireland.
Mr Juncker and Mr Tusk were not among the guests.
After the dinner, Mr Varadkar, tweeted: "Met up with Belgian Prime Minister Charles Michel and other EU colleagues in Brussels last night to talk Brexit and the future of Europe. [The] EU has stood firmly beside Ireland throughout Brexit negotiations."
The crux of their discussion was a private conversation about potential candidates for senior EU leadership positions which are up for grabs next year, but Brexit was discussed too.
The degree to which the remaining members of the EU remain united in their approach to Brexit is key to the outcome of the negotiations.
Some countries, like the Netherlands and Belgium, with closer trade ties to the UK, are concerned about the impact of a "hard" Brexit on their local economy and may push for a "softer" Brexit.
While the British Government has yet to explicitly outline the type of Brexit it wants to secure, Mrs May has repeatedly said that she wants a bespoke deal rather than opting for an "off-the-shelf" model like a Canada-style trade deal or a Norway-type relationship.
Under the so-called "three baskets" model, discussed at Chequers, the UK would, post-Brexit, place EU regulations into three baskets.
In basket one, EU regulations would be followed as if the UK were still an EU member.
In basket two, the objectives of EU regulations would be the same, but would be achieved in a different way.
And in basket three, areas where the UK would diverge completely from the EU approach.
Although seen as a possible neat compromise for divided factions of the UK Government, the European Commission has already said "the 'three baskets approach' [is] not compatible with the principles in the European Council guidelines".
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The European Commission believes that the model breaks the red-lines set by the member states of the EU.
They worry that the autonomy of EU decision-making and the integrity of the single market will be weakened and also that other countries outside the EU will seek similar bespoke arrangements, undermining the whole EU project.