The European Council will block the UK's attempt to move Brexit talks towards trade this autumn, claiming not enough progress has been made in other areas.
Although the EU's chief negotiator Michel Barnier has yet to brief the members of the council, Slovenian Prime Minister and council member Miro Cerar has said it was clear the threshold for wider talks will not be met by October, the time a decision is due.
Cerar told the Guardian: “I think that the process will definitely take more time than we expected at the start of the negotiations. There are so many difficult topics on the table, difficult issues there, that one cannot expect all those issues will be solved according to the schedule made in the first place.
“What is important now is that the three basic issues are solved in reasonable time. Then there will optimism on realistic grounds. I know this issue of finance is a tricky one. But it must also be solved, along with the rights of people.”
Brussels has been particularly frustrated by Britain’s refusal to make clear what it is willing to pay in the divorce deal, he said. Boris Johnson's comments that the EU27 could "go whistle" for the potentially "extortionate" sum - which estimates suggest will range from €20bn to €100 - had not helped concerns.
Cerar claimed the UK's "cherrypicking" had also slowed progress.
“I read the first commentaries [on the UK’s customs proposals]: ‘This is unrealistic, no way, etc’. I think it is not realistic, but in the process of negotiations every side has the right to put his proposals and the other can respond. As we said at the beginning, there can be no cherrypicking."
His comments, which support ones made by Barnier last month, come as Brexit secretary David Davis attempts to seize control of the talks with a flurry of papers due to be published this week.
It also follows an insistence by the government that enough progress will be made by October for trade talks to go ahead, after cabinet ministers privately admitted fears it could be delayed until December.
If that happens, the UK will have just 10 months to agree a transitional deal to prevent the "cliff edge" scenario feared by many businesses.