Tory Brexiteers have warned Theresa May not to give more ground to Brussels, after EU negotiators demanded Britain set out within two weeks how much it will pay for its "divorce" bill.
One Conservative former cabinet minister said EU demands were not acceptable, while another prominent backbencher said any further concessions would be a "sign of weakness".
Ms May is unwilling to anger Eurosceptic MPs where support she desperately needs, but is also eager to convince the EU she has done enough to merit moving Brexit negotiations to future trade.
The Independent EU negotiators' heads and appeal to European capitals to gain progress.
The EU's Brexit lead Michel Barnier told reporters after the latest round of talks ended on Friday that any discussion on trade would be "put back" again if Britain's position did not move in a fortnight.
He signalled that if the UK gave a commitment to pay for the money, the "sufficient progress" had been made to discuss a lucrative trading relationship.
But ex-minister John Whittingdale said: "The Prime Minister has moved quite a long way. We have made a very generous offer through her speech in Florence. "
He went on: "But the other side, Barnier and the European Commission, have essentially not budged from the position they set out at the very beginning.
"[European Union of Justice]
Tory MP Jacob Rees-Mogg talked of as a future leader in eurosceptic circles, said it was not yet time to walk away from talks but added "it is time not to be standing over".
He said: "The UK Government has so far made a number of generous concessions.
"EU desperately needs our money for the past two years of [its budget] to remain solvent."
Meanwhile, John Redwood MP said of Mr Barnier's words: "I do not mind what deadlines he sets. I do not want the Government to offer them any money at all.
"One of the things we voted for is to pay for our priorities with our own money."
Brexit talks are still largely stalemated over the dispute on how big the UK's divorce bill should be. Ms May has already indirectly committed to paying some £ 20bn, but the EU wants a concrete promise that could leave it liable to pay twice as much.
The Government had wanted to wrap up the withdrawals of the European Council summit, allowing talks to move on to transition and futher trade, but failed to largely because of the divorce bill.
If Ms May summit on 14 and 15 December, it could destabilize her leadership
The next opportunity to ensure "sufficient progress" would be in March 2018, leaving very little time for the rest of the negotiations to take place.
But The Independent understands that Ms May will not allow herself to be tied down by Mr Barnier 's Emmanuel Macron and Germany's Angela Merke l in order to push for progress in talks.
There is expected to be a flurry of diplomatic activity in the European capitals ahead of the next summit, which will see the progressive moving forward
Speaking after the close of talks on Friday, Mr Barnier was asked whether the UK only had two weeks to ensure there is more progress before the December meeting. He said simply: "My answer is yes."