Britain and the European Union proclaimed Monday a "new chapter" in relations after years of Brexit tensions as they agreed on a sweeping overhaul of trade rules in Northern Ireland.
Prime Minister Rishi Sunak and European Commission president Ursula von der Leyen adopted the deal at a meeting in Windsor, west of London.
The deal follows more than a year of tense talks over the "Northern Ireland Protocol", which has unsettled the province 25 years on from a historic peace deal that ended three decades of armed conflict.
Agreed in 2020 as part of Britain's EU divorce, the original pact kept the province in the European single market for physical goods and subject to different customs rules than the rest of the United Kingdom, angering pro-UK unionists there and eurosceptics in London.
The UK government under Boris Johnson had threatened a unilateral rewrite of the protocol unless the EU agreed to wholesale changes, souring diplomatic ties and risking a wider trade war.
"This is the beginning of a new chapter in our relationship," Sunak said at a news conference with von der Leyen, who also hailed the newly agreed "Windsor Framework".
"It's about stability in Northern Ireland. It's about real people and real businesses. It's about showing that our (UK) union, that has lasted for centuries, can and will endure," the prime minister added.
Von der Leyen said the "historic" agreement would ensure a "stronger EU-UK relationship" to tackle shared challenges such as Russia's war in Ukraine and climate change.
French President Emmanuel Macron lauded an "important decision" that will protect the European market.
And US President Joe Biden highlighted the economic opportunities that would be "created by this stability and certainty."
"Northern Ireland can accomplish the extraordinary when its leaders work together in common cause," Biden said in a statement.
Take back control
The new agreement will create "green lanes" for goods destined for Northern Ireland, and "red lanes" for goods at risk of moving on to the EU via Ireland.
Goods, including food and parcels sent to households, can travel through the green lane "without red tape or unnecessary checks", said the UK government.
"This means if food is available on supermarket shelves in Great Britain, then it will be available on supermarket shelves in Northern Ireland," Sunak said.
"We have removed any sense of a border in the Irish Sea," he added.
Paving the way for such a scheme, London agreed in January to share UK data with Brussels on the flow of goods.
Sunak also announced a new settlement on medicines, so any drugs approved for use by the UK regulator will automatically be available in Northern Ireland.
The deal will also limit, but not scrap, oversight of the arrangements by the EU's European Court of Justice (ECJ).
The protocol was agreed by Sunak's predecessor Johnson as part of his charge to pull Britain out of the EU.
He then professed surprise when the EU insisted on sticking to the letter of its requirements to treat Northern Ireland differently to Great Britain.
Attempting later to sell the deal to Conservative hardliners in parliament, Sunak turned Johnson's words from the 2016 Brexit referendum campaign back at him.
"We have delivered on what the people of Northern Ireland asked for... we have removed the border in the Irish Sea," said Sunak, urging pro-UK unionists to return to government in Belfast.
In a bid to address a "democratic deficit" within the protocol, Northern Ireland's devolved assembly will be allowed to prevent the application of new EU laws under a so-called Stormont brake.
The protocol has faced staunch opposition from the Democratic Unionist Party (DUP), Northern Ireland's largest pro-UK party, which has been refusing to re-enter the power-sharing government in Belfast for a year.
DUP concerns
DUP leader Jeffrey Donaldson said the party would now assess whether the agreement met its tests for returning to the Stormont assembly.
"In broad terms it is clear that significant progress has been secured across a number of areas whilst also recognising there remain key issues of concern," he said, noting in particular the ECJ's continuing role.
Interviewed later on Sky News, Donaldson added: "I'm determined to see this through to the end. We will take as long is required. We will not be rushed."
The Sinn Fein party, which wants reunification with Ireland and which won elections last year, urged the DUP to end its boycott of the power-sharing government at Stormont.
"I welcome the fact that a deal has been done," Sinn Fein's first minister-elect Michelle O'Neill told reporters.
"And I encourage the DUP to join with the rest of the parties and actually make politics work here."
The DUP's ultimate response could determine the reaction of Conservative eurosceptics in London, including Johnson.
Sunak said MPs would get a vote on the deal in the House of Commons "at the appropriate time". Opposition lawmakers shouted, in reference to the absent former prime minister, "where's Boris?"
Von der Leyen took in an audience with King Charles III in Windsor, stoking accusations in the UK that Sunak was trying to project a royal endorsement of the deal.
In the Northern Irish border city of Newry, some residents were eager for a breakthrough and the restoration of power-sharing.
Joe O'Hanlon, 63, added it was "about time" that elected leaders "got their act together".
Colin Smith
Simon Hannah