Negotiators have until early on Thursday morning to agree on a Brexit plan or it will not be debated at a summit of EU leaders, the First Vice-President of the European Parliament has said.
Prime Minister Boris Johnson needs to get a deal approved at the summit which starts in Brussels on Thursday if he is to avoid an almighty clash over asking for a delay to the UK’s departure.
Appearing on ITV's Peston, Mairead McGuinness said teams of negotiators for both the European Union and the UK will work throughout the night in a bid to make a breakthrough before dawn.
If no agreement by a deadline of 8am local time (7am BST) can be made, the Vice-President said, then there will be nothing for EU leaders to discuss.
With no Brexit deal yet agreed on, an extension is looking more and more likely.
The Prime Minister has repeatedly stated the UK will leave the EU on October 31 "come what may" and "do or die", but Ms McGuinness said she believed this was "impossible" with only two weeks to go,
Even if a last-minute Brexit plan is agreed on, Ms McGuinness said she believed it is "impossible and improbable" that MPs would vote it through in a special sitting of Parliament on Saturday.
On Thursday, MPs will vote on whether to sit on Saturday to scrutinise an Brexit deal, but Ms McGuinness said she did not think MPs would have ample time to scrutinise any plan to be able to vote on it.
The Irish MEP continued that EU leaders and negotiators have been turning a deaf ear to some of Mr Johnson's rhetoric as they "do not want to rush things" and are trying to be "pragmatic" and "make sure the Brexit we do [agree on] is right for everyone", rather than trying to meet a deadline.
Current legislation states that if the Prime Minister does not have a Brexit deal by Saturday and no-deal is not approved by MPs, then he must write to the EU to request a three-month extension.
On Wednesday, Brexit Secretary Stephen Barclay again confirmed that Mr Johnson will write a letter requesting a Brexit delay - as he is directed to by the - but suggested it may be possible to both send the letter and leave by the deadline.
Ms McGuinness told ITV News' Political Editor Robert Peston that the EU would be open to granting a Brexit extension if it meant allowing more time for a deal to be agreed upon.
However, Chair of the pro-Brexit European Research Group, Steve Baker, said he would prioritise leaving the EU on October 31 over getting a deal, even if one were close.
Mr Baker's comments came just hours after he and other ERG members met with the PM and he said he was "optimistic" a deal was near.
Appearing on the Peston show, Mr Baker refused to be drawn on whether he would back the PM's Brexit deal, saying he would have to "wait and see" exactly what comes out of negotiations.
Mr Johnson spent much of Wednesday trying to get the ERG and Northern Ireland's Democratic Unionist Party (DUP) to back his revised plans for the controversial backstop.
However, this plan has not been signed off by the EU.
Mr Johnson's current proposals envisaged Northern Ireland in a different regulatory framework from the rest of the UK, but a consent provision would hand the Stormont Assembly, and potentially the DUP itself, a veto on both the adoption of the system and its continuation after the transition period ends in 2020.
The EU believes this replaces the controversial Northern Ireland backstop with arrangements that are sustainable over time and are democratically supported, as requested by the UK.
The backstop was designed to avoid a hard border on the island of Ireland after Brexit and involved the UK potentially retaining a very close relationship with the EU - staying in the customs union - for an indefinite period.
Ahead of Thursday's summit, the EU's chief negotiator Michel Barnier briefed ambassadors on how talks were progressing.
Following the meeting, EU commissioner Dimitris Avramopoulos said: "Talks have been constructive but there still remains a number of significant issues to resolve."