Theresa May was visited in Brussels in the Brexit talks by EU leaders in a week of crisis in which Brexit Secretary Dominic Raab was expected, to present the negotiated agreement.
Ambassadors of the EU27, including France and Germany, said the EU European Commission They would have to examine any agreement with the British before it was published and a special summit convened.
The EU negotiator, Michel Barnier, has so far largely been released. An "optimistic" schedule would have Raab appear on Tuesday legal text agreed between the Commission and the United Kingdom Government.
During a two-hour meeting with the EU's Deputy Negotiator, Sabine Weyand, Member States' representatives insisted that they were not urged to accept the agreement between the two negotiating teams.
They explained to the Commission that they would need the best part of a week to go over the text if the growing nervousness became apparent in the face of the prospect of a withdrawal agreement selling a British Customs Union.
The development makes it less likely that a Brexit summit could be convened. EU officials have said privately that 25 November is the last possible date for a summit, and it should be convened early next week to facilitate preparations in EU capitals. It is expected that May's chief Brexit advisor Olly Robbins will come to Brussels on Sunday as there is no time to reach an agreement.
In order for the EU27 withdrawal agreement to be agreed, it must include obligations that a hard border on the island of Ireland will never be required. The EU has suggested that Northern Ireland could remain in the Internal Market and in the Customs Union. The Prime Minister has stated that she can not agree to such a "shift" in the UK and insists that the entire country remain in a temporary customs union. Brussels sets a high price for such a concession, including so-called "level playing field" commitments, to ensure that the British do not have unforeseen competitive advantages.
The frustration with the way in which the Commission has been conducting discussions with the United Kingdom is growing. They led them into the "tunnel", a time of private discussion that limited consultation with Member States.
There is particular concern about giving away a Customs Union to the United Kingdom without sufficient commitments, which will subject the United Kingdom to the EU's labor, environmental and social standards and open up its seas and fishery resources to European fleets.
A senior EU diplomat said: "The member states insisted that they can not be in the dark, it's just too important."
A senior diplomat added, "We are a long way from a moment when it comes to five o'clock" after the Commission received the information.
"Britain needs to return to London, get a clear mandate and speak again in Brussels," said an EU diplomat. "There are fluid levels. It is fluid between the Commission and the United Kingdom, and then it flows in London. "
The European Commission is expected to expand its no-deal plans in the coming days amid increasing volatility at Westminster. It will also publish laws that will exempt British citizens from their visa requirements as a third country.