The Taoiseach says there are no "a la carte" options
The European Council president 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.
Donald Tusk was speaking at a news conference alongside European Commission president Jean-Claude Juncker in Brussels.
He told reporters the British 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.
"It looks like the [have your] 'cake' [and eat it] philosophy is still alive,” he said.
"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.
Earlier, the Taoiseach Leo Varadkar 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."
A number of other EU leaders echoed Mr Varadkar's call, adding that they did not know the conclusions Mrs May and her Brexit 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 joked with reporters.
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.
"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."
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 Taoiseach and 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.
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."
Met up with Belgian Prime Minister @CharlesMichel and other EU colleagues in Brussels last night to talk #brexit and the #futureofeurope. EU has stood firmly beside Ireland throughout #brexit negotiations. pic.twitter.com/YeoMQ9PVQz— Leo Varadkar (@campaignforleo) February 23, 2018