Britain's Prime Minister Rishi Sunak will meet European Commission president Ursula von der Leyen in Windsor for final talks on changes to the problematic Northern Ireland Protocol.
Sunak will welcome von der Leyen to Windsor, west of London, at lunchtime on Monday.
A Downing Street spokesperson said that after months of talks between British ministers and EU, "constructive progress has been made" and that Sunak had won "significant and far reaching" concessions from Brussels.
Sunak said he was "giving it everything" achieve an agreement, adding: "There's unfinished business on Brexit and I want to get the job done."
One unnamed cabinet minister told journalists that the compromises to the PM were better than "any of his predecessors got" — a clear jab at Boris Johnson, who spent two years wrestling with the EU over the issue.
However, former Brexit opportunities minister Jacob Rees-Mogg warned that the "devil will be in the detail" and that the support of the Northern Irish Democratic Unionist Party (DUP) was crucial.
"There are two things we need to know: one is what the DUP thinks, because the protocol itself sets out in its first article that it is subsidiary to the Good Friday/Belfast Agreement," Rees-Mogg said. "So, if the DUP doesn't think that it meets test, that will be very influential among Conservative MPs."
"I'm afraid with all the EU deals the devil is in the detail, so when people say 'we need to see the legal text', they are not larking about, they really want to see it to understand what the effect is," he stressed.
Sunak and Justice Secretary Dominic Raab have been evasive on whether Parliament will have the final say on any deal.
The protocol, an annexe to the UK's 2020 post-Brexit withdrawal agreement with Brussels, keeps the UK's exclave of Northern Ireland within the EU's single market.
The Republic of Ireland, a member of the bloc, insisted that 'backstop' arrangement was necessary to avoid a 'hard border' with customs checks that might breach the terms of the 1999 Good Friday Agreement which ended three decades of sectarian terrorism in the north.
But that has meant customs checks on goods coming from mainland Britain and even bans on certain products like sausages and potted nursery plants. That has angered the majority unionist community, leading to unrest and a hoax bomb threat to Irish Foreign Minister Simon Coveney.
Dissident Republican groups that rejected the Irish Republican Army (IRA) making peace with the British state have also sought to exploit tensions around Brexit and the protocol to reignite violence in the six counties.
Last week, masked gunmen shot and injured a senior police detective in front of his son and other children in the town of Omagh. The Police Service of Northern Ireland suspect Republican splinter group the New IRA was behind the attack.