Rishi Sunak is to hold a Brexit summit with the president of the European Commission on Monday to sign off a revised deal on the Northern Ireland protocol.

In what could be the most perilous week of his political life, the prime minister will meet Ursula von der Leyen in the early afternoon for what No 10 billed as “final talks”.

He will then face the daunting task of selling the deal to hardline Conservative Brexiters and Northern Ireland’s Democratic Unionist party (DUP), who issued renewed warnings over the weekend that they would not be bounced into accepting something that did not meet their red lines.

While Downing Street sources said there are still matters that need consideration by Sunak and Von der Leyen, the widespread assumption is that the meeting will rubberstamp a revision to Boris Johnson’s protocol for post-Brexit arrangements in Northern Ireland.

The deal is not expected to radically change the way Northern Ireland trades with the EU via the Irish border, or with the rest of the UK, but will implement systems to ease checks across the Irish Sea – a feature of Johnson’s plan that has enraged the DUP and many Tories.

Sunak is due to host a cabinet meeting on Monday afternoon before a likely joint press conference with Von der Leyen. He will then update the Commons, where he will begin what is likely to be an extremely tough political sell.

While Tory Brexiters and the DUP have said they will only give a verdict on the revised protocol when they have read the final and full text, which might not be published until later in the week, No 10 is braced for a response that is at best suspicious and potentially hostile.

The influential European Research Group (ERG) of Brexit-minded Tory MPs has warned Sunak against trying to finalise any agreement without a formal Commons vote, which ministers have yet to commit to.

After Dominic Raab, the deputy prime minister, said on Sunday that parliament would “find a way to have its say”, Mark Francois, the Tory backbencher and ERG chair, warned it would be “incredibly unwise” to proceed without a vote.

Francois told Sky that any continued role for EU law in Northern Ireland, and thus the European court of justice (ECJ), would make the deal unacceptable – although this is inevitable given the barrier-free trade border on the island of Ireland.

“Just putting in a couple of intermediate phases, with a situation where you still end up with the European court of justice, is effectively sophistry,” Francois said.

“We’re not stupid. What we want is a situation where EU law is expunged from Northern Ireland so it is treated on the same basis as England, Scotland and Wales.”

ECJ jurisdiction in Northern Ireland would also not be acceptable to the DUP, he said, adding: “If the DUP don’t consent to the deal then it’s simply not going to fly.”

Sunak is entering into a battle of the sort that brought down Theresa May, but in a different political landscape, with many Conservative MPs more amenable to compromise, aware of slumping Tory poll numbers and desperate for a political victory.

While dissent from the DUP would be a blow to the prime minister, the Downing Street sell to Tory MPs would be for them to think beyond ideological purity and to embrace an achievement that proved beyond May and, to an extent, Johnson.

“This whole process has been based on trying to achieve something that is in the best interests of all people in Northern Ireland, and businesses there,” a government source said. “That is the lens through which the PM has approached these negotiations – with them in mind.”

Another difference is that in elections to the moribund Northern Ireland assembly in May last year, the DUP finished second to Sinn Féin and polling shows the protocol is a big concern to a minority of local voters.

The next few days are nonetheless likely to be fraught and complex, with some Conservative MPs saying that while they are open to examining the text of the deal, they fear it might be little more than a dressed-up version of the existing protocol.

“If it’s a tweak of the current arrangement it’s not really a deal, is it?” one former minister said. “If it’s the same arrangement, but just with an added instruction manual, that’s not a deal.”

As well as a vote, they said, Tory backbenchers would resist any attempts by Sunak and his team to impose an artificially accelerated timetable for agreement, in an effort to prevent proper scrutiny.

“That would be a really foolish thing to do,” they said. “It’s not just the DUP. You really need to take Conservative MPs with you, and you don’t do that by trying to bounce them into agreeing to something that they’re not happy with. That would be extremely bad politics, and I hope they’re not considering doing that.”

The talks between Sunak and Von der Leyen were announced on Sunday afternoon as a continuation of their “work in person towards shared, practical solutions for the range of complex challenges around the protocol on Ireland and Northern Ireland”.

A later No 10 statement said: “Over the past few months, there have been intensive negotiations with the EU, run by British ministers, and positive, constructive progress has been made. There have been hundreds of hours of talks covering all issues at stake and talking from first principles: what works for Northern Ireland.”

The deal is expected to address the key issue of items coming into Northern Ireland intended for the Republic of Ireland, and thus into the EU’s single market, by having most goods processed via a light-touch “green light” system to minimise checks.

While EU-facing trade necessarily requires some of the bloc’s regulations to have sway, the hope is that the reduced checks will minimise their influence, and thus the potential oversight of the ECJ.

Another change will see new rules that affected the EU’s single market requiring a final say from the devolved assembly at Stormont.