Boris Johnson will attempt to persuade MPs to back his Brexit deal later ahead of what is expected to be a knife-edge vote in the Commons on Saturday.
Mr Johnson has insisted he is “very confident” MPs will back his deal.
But the DUP’s opposition to his plans means he faces a battle to get the agreement through Parliament.
The PM is expected to focus his attention on Labour MPs in Leave-voting areas, a group of Tory Brexiteers, and rebels he expelled from his party.
Conservative Party chairman James Cleverly said conversations with the Democratic Unionist Party would also continue, despite their insistence they would oppose the deal.
Saturday’s showdown in the Commons is the prime minister’s last chance to get Parliament to approve a deal before the Brexit deadline of 31 October.
If MPs reject his plans, legislation passed by MPs says he must ask the EU for an extension until 31 January 2020 – something he has repeatedly insisted he would not do.
The BBC’s political editor, Laura Kuenssberg, said she understood the government would try to sidestep a delay and push for a general election if it was defeated on Saturday.
The revised Brexit agreement between the UK and the EU was announced at a summit of European leaders on Thursday.
Hailing the “excellent deal”, the prime minister urged MPs to “come together” to vote for his plans and “get Brexit done”.
But the DUP – whose support was seen as highly important for getting a deal through Parliament – said it would oppose the plans over concessions made by the UK to the EU on customs checks at points of entry into Northern Ireland, among other issues.
Opposition parties also confirmed they would reject the deal and instruct their MPs to vote against it.
As a result, the prime minister is expected to focus his attention on three groups:
- Tory Brexiteers who have not yet backed a deal and repeatedly voted against former PM Theresa May’s withdrawal agreement
- Twenty-three former Tory MPs who now sit as independents, including 21 Mr Johnson kicked out of the party last month after they rebelled against him in a bid to prevent a no-deal Brexit
- And a group of Labour MPs who have expressed a desire to back a deal but are concerned about protection for workers and the environment
One of these MPs, Ronnie Campbell, told the BBC’s Newsnight he was minded to back the deal.
“I think this country’s just fed up with the way Parliament’s run this for the last three years,” said the Labour veteran, who is standing down at the next election.
BBC political correspondent Nick Eardley said he understood Labour MPs who rebelled by backing Mr Johnson would not lose the whip, that is, be effectively expelled from the party.
On Thursday, Mr Johnson struck an upbeat tone about the chances of MPs backing his deal, saying: “I am very confident that when my colleagues in Parliament study this agreement that they will want to vote for it on Saturday and in succeeding days.”
Speaking about the arithmetic of getting the deal through Parliament, Conservative Party chairman James Cleverly told the BBC: “If everybody sticks to their word and votes the way they said they would if a deal was presented then we’ll have the numbers to get through.”
The new deal is largely the same as the one agreed by Theresa May last year – but it removes the controversial backstop clause, which critics say could have kept the UK tied indefinitely to EU customs rules.
Northern Ireland would now remain in the UK’s customs union, but there would also be customs checks on some goods passing through en route to Ireland and the EU single market.
The DUP’s deputy leader, Nigel Dodds, accused the prime minister of being “too eager by far to get a deal at any cost”.
He predicted a “massive vote” against the deal on Saturday, adding that the DUP expected to “play a crucial role” in amending the legislation.
Can Boris Johnson win the vote?
The winning post for votes in the House of Commons is 320 if everyone turns up – seven Sinn Fein MPs do not sit and the Speaker and three deputies do not vote.
There are currently 287 voting Conservative MPs. The prime minister needs to limit any rebellion among them.
Then, if the DUP will not support his deal, he will need the backing of 23 former Conservative MPs who are currently independents. Most will probably support the deal, but not all.
That is still not quite enough, though, so the PM will also need the backing of some Labour MPs and ex-Labour independents. In March, when MPs voted on Theresa May’s deal for the third time, five Labour MPs backed it, plus two ex-Labour independents.
This time it is likely to be a bit higher than that because several MPs have said they would now back a deal.
All this still leaves the vote very close. And it is possible some MPs could abstain, making it even harder to predict the outcome.
Meanwhile, Scotland’s highest civil court, the Court of Session, is set to consider a legal bid to block Mr Johnson’s deal.
Anti-Brexit campaigners believe the deal contravenes existing legislation preventing Northern Ireland forming part of a separate customs territory to the rest of the UK.
Elsewhere, the SNP has tabled an amendment to Mr Johnson’s deal demanding an immediate extension to the 31 October deadline and a general election.
The SNP’s parliamentary leader, Ian Blackford, said opposition parties need to “quit dithering, back our amendment, and finally act to bring this appalling Tory government down and stop Brexit”.
And former Prime Minister David Cameron has said he would have backed the deal if he was still an MP.
“I hope he’ll get it through Parliament. I suspect he will but it will be tight.”