Theresa May is holding talks with European Commission president Jean-Claude Juncker in Brussels as she attempts to agree the outline of the UK's future relationship with the EU.
The prime minister needs to strike an agreement on a framework in areas like trade and security in order to avoid derailing a Brussels summit on Sunday, at which her draft withdrawal agreement will be discussed.
Sky News has learnt the PM's cabinet agreed she should adopt bolder language in tonight's talks to flesh out the political declaration on the future relationship between the UK and EU.
The current document is just seven pages long, but senior ministers were shown a secret 20-page draft that form the basis of the meeting between Mr Juncker and Mrs May.
Mark Stone, Sky News' Europe correspondent, said several sources were suggesting Angela Merkel could refuse to attend the summit on Sunday unless there is a deal to sign.
He added that if negotiations continue past Friday then the hope of "rubber stamping" an agreement by the deadline would fall through.
Earlier, Mrs May has appeared to contradict herself over what will happen if MPs reject her Brexit deal in the Commons.
During fractious exchanges in PMQs, the prime minister was asked by former cabinet minister Esther McVey if Britain would leave the EU "come what may".
Mrs May told the Commons that "the United Kingdom will leave the European Union on 29 March 2019".
But earlier in the session, when asked what would happen if MPs vote down the deal, she replied: "If you look at the alternative to having that deal with the European Union it will either be more uncertainty, more division or it could risk no Brexit at all."
A Downing Street spokesperson later said Mrs May had been "clear on her determination" to leave the EU as scheduled.
When asked if no deal was still a possibility, they replied: "Yes. The only thing certain is that if we don't go forward with an agreement is that there will be uncertainty - no deal on one hand, no Brexit on the other."
The apparently contradictory answers came after Work and Pensions Secretary Amber Rudd said parliament will not allow a "no deal" divorce to happen.
She also said in a BBC radio interview that "Brexiteers may lose their Brexit".
During PMQs, Labour leader Jeremy Corbyn accused Mrs May of overseeing a "shambles" in Brexit talks.
"It fails the prime minister's red lines, fails Labour's six tests, and it fails to impress the new Northern Ireland minister (John Penrose), who just hours before he was appointed said the deal is 'dead'," the Labour leader told MPs
"Instead of giving confidence to the millions of people who voted both Leave and Remain, this half-baked deal fails to give any hope that it can bring the country together again.
"Isn't it the case that parliament will rightly reject this bad deal, and if the government can't negotiate an alternative then it should make way for those who can and will."
The PM claimed Mr Corbyn had failed to read the contents of the deal, replying: "Never mind a second referendum, he hasn't got a first clue."
She added: "He's telling Leave voters one thing and Remain voters another - whatever (Mr Corbyn) will do, I will act in the national interest."
As well as criticism from Labour, the PM faced Tory demands to renegotiate her Brexit deal.
Brexiteer Andrew Rosindell told her he was "deeply unhappy" with the withdrawal agreement and urged her to lead the country in a new direction by "completely cutting away the tentacles" of the EU.
Neil Parish, who is chair of the environment, food and rural affairs committee, expressed his disquiet over the Irish border backstop.
He claimed it "threatens the integrity of the UK" and advised the PM to listen to concerns raised by MPs.
Nigel Dodds, the Democratic Unionist Party's Westminster leader, accused Mrs May of "deleting" previous assurances over the Irish border issue.
He said: "In the December joint report agreed between the European Union and the United Kingdom it was agreed that Northern Ireland would have the final say on whether or not it diverged from the UK single market and was subjected to single market European rules with no say, why has the Prime Minister deleted all reference to that in the withdrawal agreement?"
Mrs May responded: "The December joint report referred to a decision being taken by the Northern Ireland Executive and Northern Ireland Assembly which sadly we do not have in place today."