SIGNIFICANT issues remain unresolved in the Brexit negotiations, which have entered the final day before Boris Johnson attempts to sign off on a deal during the key EU summit, starting tomorrow.

Officials on both sides of the Channel said this morning that numerous obstacles still needed to be surmounted for a fresh agreement to be brokered.

The Prime Minister needs to get a deal approved at the summit of EU leaders starting in Brussels on Thursday if he is to avoid an almighty clash over asking for a delay to the UK's departure.

Stephen Barclay, the Brexit Secretary, confirmed that Mr Johnson would write a letter asking for an Article 50 extension if no deal was in place by Saturday, something the PM has repeatedly ruled out.

One suggestion has been that the PM might follow this letter with another, effectively negating the request. When asked if there could be a second letter, Mr Johnson’s spokesman said: “I can’t go into that.”

Talks in Brussels resumed this morning after running into the early hours in a previous session.

The PM's spokesman said there "certainly remained issues to resolve", a sentiment echoed by EU Commissioner Dimitris Avramopoulos.

After a briefing by EU chief negotiator Michel Barnier, Mr Avramopoulos said: "Talks have been constructive but there still remains a number of significant issues to resolve."

Irish Taoiseach Leo Varadkar said he was "confident" a deal could be struck by the current deadline and raised the prospect of another EU summit being held in the coming weeks.

READ MORE: Brexit talks to resume on final day before crunch EU summit 

But he warned there were still numerous hurdles in the way after speaking with Mr Johnson and the European Commission this morning.

"There is a pathway to a possible deal but there are many issues that still need to be resolved, particularly around the consent mechanism and issues around customs and VAT," he said.

"Although time is running short I am confident these objectives can be achieved."

Mr Johnson will chair Cabinet at 2.30pm, brought forward from 4pm but Downing St insisted nothing should be read into this. Michel Barnier, the EU’s chief negotiator, will brief EU ambassadors around the same time.

The PM is also set to have more talks with the Democratic Unionists and the Tory Brexiteers of the ERG group before he addresses the Conservatives’ 1922 backbench committee scheduled for 7.30pm.

A split among the hardliners has emerged as it was suggested Mr Johnson might be willing agree to a customs and regulatory border down the Irish Sea.

Owen Paterson, the former Northern Ireland Secretary, said it was "unacceptable" that a custom border could be created between Northern Ireland and Great Britain.

However, Jacob Rees-Mogg, the Commons leader and a former ERG chairman, believes an agreement could be accepted by MPs, telling LBC: "The votes are there now for a deal."

The DUP has helped prop up the Tory administration following increased funding from Mr Johnson's predecessor in No 10 as part of a confidence and supply deal, in a £1 billion package branded as a "bribe".

There is speculation more money could be headed in the way of Arlene Foster's party as the PM tries to get them on board with any concessions.

The DUP were decidedly lukewarm on the mooted proposals in a statement after their second audience with the PM in as many days, with a spokesman saying "gaps remain and further work is required".

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David Davis, the former Brexit Secretary, said DUP backing would be influential for his colleagues.

"There will be quite a lot of Tory MPs who will take their line from what the DUP do," he told BBC Radio 4's Today programme.

It is thought that it is more likely than not that the Government will table a motion by close of play today to call for a Saturday sitting of the Commons. This is the day that, under the Benn Act, Mr Johnson has to write to Brussels asking for a delay if Parliament does not agree to a deal by then. Sources suggested that Labour and the Liberal Democrats will tomorrow vote against having such a sitting as it is not required under the extension legislation.

Appearing before the Commons Brexit Committee, Mr Barclay reiterated that the PM would write to Brussels asking for an Article 50 extension, as previously revealed in documents submitted during a Scottish court challenge.

"I can confirm, as the Prime Minister has repeatedly set out, that firstly the Government will comply with the law, and secondly it will comply with undertakings given to the court in respect of the law," he said.

The Secretary of State confirmed that the Government "will abide by" what is set out in that letter, following fears the PM could try to scupper an extension with a second contradictory letter or request to a member state to block an extension.

Mr Barclay reiterated the Government's commitment to leave the EU on the current October 31 deadline, despite the act demanding a delay to the end of January if MPs to do not approve a deal by Saturday.

If Mr Johnson succeeded in bringing a deal home to the UK, he would then face a battle to do what Theresa May failed to do three times and get it approved by Parliament in what has already been dubbed “meaningful vote four”.

Jeremy Corbyn said he was "deeply concerned" about the negotiations and ruled out his party backing a deal under the PM's reported terms.

Pressure to sign off on a draft agreement is peaking. A legal text needs to be published ahead of the summit if the EU27 are to consider ratifying the Withdrawal Agreement at the two-day summit.

Their approval would allow Mr Johnson to put the deal to MPs in a proposed extraordinary sitting of Parliament on Saturday.

During the weekend session, MPs would be able to back or reject any deal presented to them or discuss what to do next in the Brexit saga.