Prime Minister Keir Starmer has arrived at the first UK-EU summit after striking a major reset deal with the EU on Monday.
Government sources said talks were “down to the wire” on Sunday but the result was a major breakthrough.
It is understood that a deal has now been approved by the EU ambassadors’ committee.
Government sources said “huge progress” has been made in agreeing “a mutually beneficial deal with the EU” that would “deliver for British working people”.
But they said the Prime Minister has been “clear that he will only agree a deal which delivers in the national interest of the United Kingdom”.
Details are expected to be announced at the first UK-EU summit on Monday, where the Prime Minister will meet European Commission president Ursula von der Leyen for the second time in four days.
Foreign secretary David Lammy has arrived for the summit as well.
An announcement is expected on defence and security, which could feature an agreement allowing British firms access to a £125bn (150 billion euro) EU defence fund.
Deals on allowing British travellers to use e-gates at European airports, cutting red tape on food exports, and setting up a youth mobility scheme with the EU, are also thought to be on the table.
But reports suggested disagreements over fishing rights and youth mobility have presented last-minute stumbling blocks.
However, the Scottish Government says it has not seen the new deal on fisheries with the EU.
A Scottish Government source said a briefing on talks was requested last week, but was not provided by the UK Government.
It is understood that several recent scheduled meetings between UK and Scottish ministers to discuss fisheries have not gone ahead.

Insight Paris Gourtsoyannis Westminster Correspondent
The Scottish Government says it has not seen the new deal on fisheries with the EU, expected to be unveiled today.
Wide-ranging “reset” talks between the UK and EU are believed to cover fisheries, with Brussels demanding expanded access and management of British fishing waters.
While international negotiations are reserved to the UK Government, agriculture and fisheries are devolved to Scotland.
However, STV News understands the Scottish Government has not been briefed on negotiations or the content of any draft deal.
Talks between UK and EU negotiators went on late into Sunday night ahead of a summit today, when Prime Minister Keir Starmer and EU Commission President Ursula von der Leyen are expected to sign off a deal aimed at improving post-Brexit trade terms.
The deal is also expected to include a youth mobility scheme, and deeper cooperation on defence and military procurement.
But there has been concern in the fishing industry about concessions being considered by UK ministers to secure a deal.
A Scottish Government source said a briefing on talks was requested last week, but was not provided by the UK Government.
It is understood that several recent scheduled meetings between UK and Scottish ministers to discuss fisheries have not gone ahead.
EU member states are regularly briefed by officials on the status of negotiations.
Following his election last year, Keir Starmer said he had “reset” relations with the Scottish Government. Referring to that comment, a Scottish Government source said: “So much for the reset.”
Both Conservative leader Kemi Badenoch and Reform UK leader Nigel Farage have already described the deal as a “surrender”, despite the details not yet being known, and indicated they would tear it up if they came to power.
Youth mobility could prove a major sticking point for the Opposition, and Badenoch said she feared it would involve a return to free movement “by the back door”.
The Tories have also set out a series of “red lines” on fishing rights, including ensuring exclusive access to Britain’s territorial sea and resisting “a multi-year agreement which only benefits France”.
The Liberal Democrats said Britain should not to be “dragged back” to “the Brexit wars of the past”, and leader Ed Davey compared Badenoch and Farage with “dinosaurs fighting old battles”.
He said: “Keir Starmer must be bold and ambitious for our country in today’s summit. Voters were promised change by this Government and they have to deliver.
“Being truly ambitious, including a new UK-EU customs union, would be the single biggest thing ministers could do to boost public finances.
“Anything less would be a choice to limit growth, harming living standards and hitting the NHS and other public services.”
Conservative peer Lord Rose said the Government’s deal with the EU was a “win” and should not be described as a surrender.
The former chairman of Marks & Spencer told Times Radio: “It has to be a win… it’s five years since we did the deal in 2020. But in reality, look what has happened in the world since then. There’s been massive global change. And the UK is finding itself increasingly stranded now. And we’ve got to find a role for ourselves.”
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