Rishi Sunak is poised to announce a deal to end the protracted row over the post-Brexit Northern Ireland protocol as soon as Monday, the Guardian has been told. The move would come after four months of intense negotiations and mark an end to a two-year standoff with the EU. But in a huge political gamble for the prime minister, it may trigger a fresh battle with pro-Brexit Conservative backbenchers in the European Research Group (ERG) and the Democratic Unionist party (DUP). Tentatively said to have been named the “Windsor agreement”, the deal would overhaul post-Brexit arrangements in Northern Ireland. No 10 hopes it will also pave the way for the re-establishment of an assembly in Stormont given power-sharing has been suspended since the DUP’s first minister resigned over the protocol in February 2022. According to reports on Friday night, Ursula von der Leyen, the European commission president, was scheduled to meet King Charles on Saturday as a final flourish in sealing the deal but that was cancelled earlier in the day. MPs have been put on a three-line whip to attend parliament on Monday and cabinet ministers are braced for a potential conference call over the weekend. Discussions are still under way in Downing Street about inviting Von der Leyen to the UK for a handshake to seal the deal. Von der Leyen and Sunak spoke on Friday afternoon – their third meeting in a week – fuelling speculation that a deal was at the “presentation” stage. Downing Street sources did not confirm whether a deal would be announced in the coming days, but stressed talks were continuing and that any discussion of timings was “purely speculative”. Earlier this week, prominent MPs in the ERG, including its deputy chair, David Jones, warned that if Sunak’s deal involved a tweak of the existing arrangements it would amount to nothing more than a “glossary on how to implement the protocol”. The group has said it is in “lockstep” with the DUP, which has indicated it will not support the deal unless it ends the application of EU law in Northern Ireland, which is the bedrock of the protocol and highly unlikely to happen. Government sources claimed the prime minister was relaxed about the threat of a backlash from the ERG and the DUP because he believed the deal would address all their concerns including checks on goods and food produce entering Northern Ireland from Great Britain and the constitutional right to be treated the same as any other country within the UK on trade matters. The Northern Ireland secretary, Chris Heaton-Harris, held an unscheduled meeting with the EU’s chief Brexit negotiator, Maroš Šefčovič, on Thursday, according to one insider. They said Heaton-Harris was determined to go for the face-to-face summit to reassure Brussels the UK government was “fully aware” of the ERG’s anxieties and would be pressing ahead despite the backlash. “This was a reassurance mission, not a rescue mission,” the source said. Heaton-Harris is seen as an experienced judge of the mood of the party, having served as chief whip previously. But concerns in Downing Street are growing that Boris Johnson could double down on the critical intervention he made about Sunak’s handling of the Brexit negotiations last weekend. Sammy Wilson, the DUP’s Brexit spokesperson, said the former prime minister was helping the ERG and unionists ensure the Northern Ireland protocol bill, which would allow the UK to unilaterally rip up some Brexit arrangements for Northern Ireland, made it to the statute books. It was Johnson who agreed the protocol deal in October 2019, in order to bolster his chances at the December election with his claim of an “oven-ready Brexit” for the electorate. The bill is seen as a backstop to ensure the protocol is overhauled, but it has been paused in parliament since mid-October and the EU has pushed for it to be dropped. Wilson told the Chopper’s Politics podcast that Johnson had a “duty to help because after all he was the person who got us into the situation”. On Friday, the foreign secretary, James Cleverly, told Times Radio he hoped any deal, if it were sealed, would address all the conditions laid down by the DUP. “When, hopefully, we get those issues resolved then I would hope that the DUP would recognise that we’ve addressed their concerns and until we have addressed those concerns we’re not going to sign off on the deal,” he said. The comments signalled a reluctance by some in government to press ahead without agreement from the DUP, and risked rattling senior EU figures. Those involved in the negotiations have tightly guarded the substance of the deal but informed sources said it involved a “carve out” for all goods that could be shown to be consumed within Northern Ireland. This would give suppliers to supermarkets, corner shops, canteens in hospitals and schools the right to trade as they did before Brexit with no customs declaration or security and safety certificates. In order to enforce it, there would be hefty fines for any businesses caught smuggling non-compliant goods into Northern Ireland and then exporting them on to the EU. There is also expected to be a fudge on the role of the European court of justice, removing the EU’s right to automatically go to the court in the event of a claimed “infraction” of EU law. The agreement is expected to include the establishment of an arbitration panel involving Northern Irish and EU judges as the first port of call in the event of a dispute, with Northern Irish courts having a say over public health issues. It is not believed that the deal includes a new arrangement to safeguard the supply of medicines to Northern Ireland. Sunak hinted on Wednesday that MPs would get a say on any agreement, but No 10 later clarified that the prospect of a vote remained “hypothetical” until a deal was struck. On Friday, a House of Lords committee warned the foreign secretary not to forget the problems with the supply of medicines to Northern Ireland in their protocol negotiations. In a 30-page letter they said claims that the medicines supply issue was fixed last year with fresh EU legislation are not true. “The evidence we received from industry stakeholders makes clear that this is far from the case,” said Michael Jay, the chair of the protocol committee.