AN historic Brexit deal could finally be sealed today as UK and EU officials scramble to nail down the final details of a new withdrawal agreement that would see Britain leave the European Union on October 31.

Downing St sought to play down expectations of a dramatic late night breakthrough, admitting “thorny issues” remained that would take the negotiations into Thursday.

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These were said to centre on Northern Ireland and the issue of consent, most notably concerns by the Democratic Unionists over the right of local politicians to be able to veto new customs arrangements with the EU. The matter of how to prevent fraud in Value Added Tax was also said to be a sticking point.

The Herald: Camley's Cartoon: Boris Johnson closes in on Brexit deal.Camley's Cartoon: Boris Johnson closes in on Brexit deal.

One Government source made clear there would be no deal agreed on Wednesday night due to such unresolved issues.

“Everyone will be working into the night but there won’t be a deal this evening," he explained.

Michel Barnier, the EU’s chief negotiator, briefed European ambassadors about the state of play but again no expectation emerged of an imminent deal being sealed. Intensive talks were set to continue through this morning as EU leaders prepared for the start of the European Council this afternoon.

The agenda could be changed to push Brexit back to Friday to allow negotiators more time.

Yet, there were positive noises from across the continent that a deal could be only hours away.

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Donald Tusk, the European Council President, said: "The basic foundations of an agreement are ready and, theoretically, tomorrow we could accept this deal with Great Britain and avoid the chaos and the misfortune linked to an uncontrolled, chaotic exit.”

Following a bilateral meeting in Toulouse, Angela Merkel described the negotiations as being in the “final sprint” and said she was “increasingly of the belief” an agreement would be reached with the UK.

Her host, Emmanuel Macron, the French President, said he shared the German Chancellor’s optimism, adding: “I hope that agreement will be found in the coming hours.”

Last night as the UK Government tabled a motion to allow Westminster to sit on Saturday to vote on any new deal, anti-Brexit campaigner Jolyon Maugham announced he intended to launch a legal action at Edinburgh’s Court of Session to stop Boris Johnson from putting a new Withdrawal Agreement before MPs.

Saying he expected his petition to be heard on Friday, the QC claimed the expected new Withdrawal Agreement would be contrary to section 55 of the 2018 Taxation [Cross-border Trade] Act, which states: “It shall be unlawful for Her Majesty’s Government to enter into arrangements under which Northern Ireland forms part of a separate customs territory to Great Britain.”

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Jenny Chapman, the Shadow Brexit Minister, said she expected Labour would support any amendment put forward to attach a confirmatory referendum to any Brexit deal.

Speaking to the BBC's Andrew Neil Show, she said: "The expectation would be that should a deal be tabled on Saturday, and we don't know that is going to happen, I am as sure as you can be that there will be an amendment tabled that would want to see a referendum attached to the deal."

Former Tory MP Anna Soubry, who now leads the Independent Group for Change, denounced the amount of time MPs would have to scrutinise Mr Johnson's deal on Saturday with a debate scheduled from 9.30am to 2pm.

She tweeted: "It is increasingly clear Johnson's 'new' deal is worse than May's. Parliament will get five hours’ debate on Saturday without any independent assessments, analysis or select committee scrutiny of the most important set of decisions we will make in generations. That's plain wrong."

Earlier, the Prime Minister told Cabinet colleagues there remained a “chance to get a good deal” and later, addressing Tory backbenchers in the Commons, likened securing a Brexit deal to climbing Mount Everest.

“He was talking about being on the Hillary Step on our way up to Everest but the summit is still shrouded in mist,” Steve Baker, the ardent Brexiteer, told reporters after the conclusion of a meeting of the Conservatives’ backbench 1922 committee.

The former Brexit minister said he had been reassured on the DUP’s red-lines being respected.

“The DUP’s red-line is that the whole of the UK needs to leave the customs union and be in its own single customs territory and the PM has just told us that is what he is going to do,” he explained.

“The other DUP’s other most important red-line is consent in relation to regulatory alignment and that I understand will also be carried through; the PM made it clear,” insisted Mr Baker.

He brushed aside concerns that a customs and regulatory border would emerge down the Irish Sea, saying he would “not accept any allegation of a sell-out on the Union”.

The Buckinghamshire MP also dismissed talk in Brussels that an indicative vote by MPs on the principles of a Brexit deal would suffice. It had to be a meaningful vote, he insisted.

“Until there is a legal text we are not going to make a decision. We have come this far. Eurosceptics always pay attention to meticulous and tedious analysis of legal texts and that’s what we will do this time as well,” added Mr Baker.

Following the 1922 meeting, Alister Jack, the Scottish Secretary, told The Herald that he was "optimistic" a deal would be struck. Asked why, he replied: "Because we are very close."

Meanwhile during a session of the House of Commons Brexit Committee, Joanna Cherry, the SNP’s justice spokeswoman, claimed that, unlike the DUP and the Conservative ERG group, the Scottish and Welsh Governments were not being kept informed of ongoing developments and were “out of the loop”.

Stephen Barclay, the Brexit Secretary, replied by saying Government ministers had been to Edinburgh “within the last week” to engage with the SNP administration.

But Ms Cherry, who represents Edinburgh South West, was unimpressed, stressing how events were moving apace and tweeted later that the Scottish Government was being “kept totally in the dark”.