UK Prime Minister Boris Johnson and European Union (EU) Brexit negotiator Michel Barnier announced a revised Withdrawal Agreement this morning.

They did so after what German Chancellor Angela Merkel called a “final sprint” yesterday, which was dominated by intensive discussions between Johnson and the Democratic Unionist Party (DUP) seeking their agreement on a proposed deal that would mean a customs border running down the Irish Sea.

This is something Johnson’s predecessor, Theresa May, had said no British prime minister could agree to. The DUP’s holding out created great difficulties for Johnson in getting his deal agreed by the UK parliament as planned at a scheduled “Super Saturday” sitting following the EU summit.

Conservative Party leader Johnson, who leads a minority government, needs 320 MPs to agree his deal. The DUP has long been viewed as a kingmaker, with its 10 MPs part of Johnson’s arithmetic and the Tory’s 60 strong pro-Brexit European Research Group (ERG) and particularly the 28 hard-line “Spartans,” considered unlikely to agree any deal unacceptable to the unionists.

This morning the DUP issued a statement that it could not support Johnson’s proposed deal, but would “continue to work with the government to try and get a sensible deal that works for Northern Ireland and protects the economic and constitutional integrity of the United Kingdom.” It was clearly angling for further concessions, rather than closing the door on an agreement.

Johnson responded instead by dropping a proposed veto for the DUP on any deal that was contained in his original proposal. Barnier outlined an agreement he said could now be passed by October 31, the existing Brexit deadline. It would keep the border between Northern Ireland and the Republic of Ireland open, preserving the all-island economy, protecting the integrity of the single market and keeping Northern Ireland in the UK’s customs territory.

It would, however, mean checks on the border so that UK authorities can apply tariffs to goods coming from third countries and the EU can do so if they might enter the Single European Market.

President of the European Commission Jean-Claude Juncker sent a letter to the president of the European council, Donald Tusk, stressing that it was now time for Britain’s parliament to do its part. However, there is no chance of Labour, the Liberal Democrats, the Scottish National Party and other pro-Remain parties backing the deal with Jeremy Corbyn describing it as “an even worse deal than Theresa May’s, which was overwhelmingly rejected.”

To secure a majority, Johnson needs the ERG to agree to also abandon the DUP, unless the unionists can be bought off with billions in subsidies. He will also need most of the 21 Tories Johnson, expelled last month for their efforts to block a no-deal Brexit, to back a deal rather than risk no-deal, a general election or a second referendum they may lose.

Ultimately success would only be possible with support from Labour MPs who have made clear they want no part of a second referendum that would be massively unpopular in their pro-Leave constituencies but do not want to risk a no-deal outcome. Labour MP Stephen Kinnock claims that the number ready to vote with Johnson is as high as 30. Some pro-Remain MPs might vote with the government if there is a promise of a “confirmatory ballot” second referendum that would pitch Johnson’s deal against staying in the EU.

In such fraught circumstances, Johnson is pressing home his advantage against a deeply divided parliamentary Remain bloc which has itself been abandoned by the EU.

How they respond cannot be predicted. But divisions in the Labour Party have become a central concern for Britain’s pro-Remain ruling elite.

There are opposed positions on how to respond to Johnson’s agreement, especially on how best to sideline Corbyn’s proposal that he first leads a “caretaker government” to block Brexit and then seek a general election before negotiating Labour’s own Brexit deal and holding a second referendum. This is official party policy after September’s annual conference.

There is little to suggest Corbyn will be elevated to caretaker prime minister by the Liberal Democrats, the small Change UK group and pro-Remain dissident Tories supporting a no-confidence vote. Lib Dem leader Jo Swinson continues to state that Corbyn doesn’t have the numbers and is unfit to be prime minister anyway, and this would be more unlikely still now Johnson has an agreement.

The calculations of the Remain camp in avoiding precipitating a general election have been based on expectations that Johnson will defy the Benn Act, which forces him to seek an extension of the Brexit deadline until January next year if there is no deal or parliament rejects his deal. But there are now reports that Johnson will bypass this by sending a letter to the EU asking it to reject appeals for an extension instead.

None of this affects the insistence of pro-Remain MPs, led by Labour’s Blairites, that a second referendum must take place before any general election. The start of this week was dominated by reports that Corbyn’s key ally, Shadow Chancellor John McDonnell, was now working with the Blairites to overturn Corbyn’s policy and even engineer his downfall in a “silent coup.” Denials have inevitably followed, including McDonnell declaring at a Labour rally Monday evening, “We just have to tell the media out there: they will never divide us.”

Before this public show of unity, however, Unite the Union, the Transport Salaried Staffs’ Association (TSSA) and Communication Workers Union (CWU) were issuing formal complaints to Labour’s general secretary, Jennie Formby, protesting 37 members of Corbyn’s staff being summonsed to “informal meetings” headed by McDonnell ally, Sir Bob Kerslake, about their future roles in his office.

There was a meeting of the Parliamentary Labour Party earlier Monday, in which Corbyn loyalists Ian Lavery and Andrew Gwynne--in charge of coordinating Labour's election campaign--told MPs the party had “never been in better shape” for a snap poll. One MP told the Politics Home website that Lavery only “united the PLP in one clear unambiguous position: we cannot have an election.” Kevan Jones MP reportedly asked Mr Lavery and Gwynne, “What colour is the sky on your planet?” while another said, “Half of us think we will lose to the Lib Dems, the other half are looking over their shoulders at the Brexit Party.”

Last night, Shadow Brexit Minister Jenny Chapman said she expects Labour would support any amendment put forward Saturday to attach a confirmatory referendum to a Johnson deal.

Corbyn is left, as usual, straining to maintain unity with his party’s right-wing MPs and protecting them from the party’s membership. He closed Monday’s rally, speaking directly to the Blairites, McDonnell and his other main backer, Shadow Home Secretary Diane Abbott, by pledging, “I want to bring the movement and the party together. That has been my whole objective during this whole saga over Brexit.”

Yesterday he was busy placating his pro-Brexit faction, telling the media that Labour MPs who back Brexit will not have the whip removed as he believed in the "power of persuasion rather than the power of threat.”

This will do nothing to please the dominant pro-Remain faction but will convince them they can continue to do whatever they want under Corbyn’s protection.

Whatever happens Saturday, the Liberal Democrats have tabled an amendment to the Queen's Speech requiring that any Brexit deal is put to a “People's Vote.” There will almost certainly be a large vote in favour on Labour’s benches, even if Corbyn whips against it. Meanwhile Corbyn’s central leadership core will continue to break apart, with the Skwarkbox website reporting that Labour’s pro-Brexit “northern MPs are now in discussions to build on their successful rearguard action” against McDonnell and Blairites Tom Watson and Sir Keir Starmer, “by caucusing as a parliamentary bloc” against “an attempted ‘remainer take-over’.”