Smiling Rishi Sunak and Ursula von der Leyen launched the hard sell this afternoon after shaking hands on new Brexit rules for Northern Ireland.

The PM and EU commission president hailed the package at a press conference after confirming the culmination of months of painstaking negotiations.

Mr Sunak said they had achieved a ‘decisive breakthrough’ and forged a ‘Windsor Framework’ – named after the location of their talks.

He insisted the settlement could open a ‘new chapter’ in ties with the EU.

‘I believe we have found ways to end the uncertainty and challenge for the people of Northern Ireland,’ Mr Sunak said.

Mr Sunak promised ‘smooth flow of trade’ between mainland Britain and Northern Ireland. He argued that the minimum of EU rules would be followed to avoid a hard border with the Republic, and a ‘Stormont Break’ will mean laws cannot be forced on the province. 

Downing Street has boasted of ‘significant and far reaching’ concessions, and there are bombshell rumours this afternoon that the DUP is ready to shift position and accept the agreement.

The reports come despite the unionists having set red lines that looked very difficult to meet – including completely removing the role of the European Court of Justice. Having the DUP on board would pave the way for the restoration of powersharing at Stormont. 

Party leader Jeffrey Donaldson played down the claims in the Irish News, tweeting: ‘We’ll take our time to consider the detail and measure a deal against our seven tests.’

In other positive noises for Mr Sunak, Northern Ireland minister and self-styled ‘Brexit hard man’ Steve Baker – who has been on ‘resignation watch’ over the past few days – said this afternoon that the government is on the verge of a ‘fantastic’ deal. 

Cabinet signed off the plans this afternoon, after the one hour and 45 minute meeting between Mr Sunak and Ms von der Leyen.

But Mr Sunak could still face a rough ride from Tories when he makes a statement to the Commons this evening.

The PM’s allies are waiting nervously to see how Boris Johnson will react to the revised terms, with fears he could intervene in the debate.

Meanwhile, the government is facing a furious backlash for dragging the King into the political pressure-cooker – as Charles will meet Ms von der Leyen separately this afternoon during her visit. 

Brussels is thought to have agreed to ditch checks and paperwork on almost all goods and produce sent from mainland Britain to Northern Ireland. Red and green customs channels will be used to distinguish what is bound for the province and the Republic, which remained inside the EU 

Mr Sunak is believed to have secured a package that removes single market rules from 90 per cent of products made in Northern Ireland, as long as they are not bound for the EU.

Although Northern Ireland might still be covered by future EU legislation, there will be a democratic mechanism – a ‘Stormont Lock’ – intended to ensure the province’s politicians have a say and consultation with London.

In one of the potential flashpoints, the European Court of Justice will stay as the final arbiter on single market rules in Northern Ireland. But there will be protections designed to demonstrate that cases cannot be referred directly by the EU.

Mr Sunak appears to have had a crucial win by persuading the bloc that the text of the protocol should be tweaked – something it had previously refused to do. 

Sir Jeffrey said before the announcement: ‘I’m neither positive nor negative. I think we need to take time to look at the deal, what’s available, and how does that match our seven tests.’ 

Tory Eurosceptics were largely keeping their powder dry this morning.

But Mr Baker moved to quash rumours he will quit after another bout of talks in No10. 

He told broadcasters: ‘I can only say this: that the Prime Minister is on the cusp of securing a really fantastic result for everyone involved.’

In a round of interviews this morning, Jacob Rees-Mogg did not rule out backing the plan, but suggested Mr Sunak will fail to win over the DUP.

The ex-Cabinet minister told ITV’s Good Morning Britain: ‘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.

‘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.’

Ms von der Leyen is also holding talks with King Charles during her visit to Windsor.

That has caused a wave of anger among DUP and Eurosceptic figures that the monarch is being dragged into the contentious politics of Brexit.

Buckingham Palace seemed to point the finger at ministers by saying the government had advised that the King should meet the visiting dignitary.

Ex-DUP leader Arlene Foster tweeted: ‘I cannot quite believe that No10 would ask HM the King to become involved in the finalising of a deal as controversial as this one. 

‘It’s crass and will go down very badly in NI. We must remember this is not the King’s decision but the Government who it appears are tone deaf.’ 

Mr Rees-Mogg said was ‘constitutionally unwise’ for the King to meet EU chief Ursula von der Leyen around the signing of the new post-Brexit deal on Northern Ireland.

The leading Conservative Brexiteer said: ‘It is surprising that the King will meet Ursula von der Leyen today as it antagonises the people the Prime Minister needs to conciliate.

‘It is also constitutionally unwise to involve the King in a matter of immediate political controversy.’

The PM’s official spokesman said Rishi Sunak believes ‘fundamentally’ the decision was for Buckingham Palace.

‘He firmly believes it’s for the King to make those decisions,’ the official said.

‘It’s not uncommon for His Majesty to accept invitations to meet certain leaders, he has met President Duda and President Zelensky recently. He is meeting with the president of the EU today.’

Asked why the final protocol talks were taking place in Windsor, the spokesman said: ‘There are a number of occasions when these sorts of talks have been held in significant occasions, this is no different.’

Downing Street has stressed that there are still substantive issues for the PM and Ms von der Leyen to address this afternoon, although they are thought to have tied up the main elements in talks by phone yesterday.

Irish deputy leader Micheal Martin has praised ‘very significant and substantial progress’ in protocol negotiations between the UK and EU.

‘I think we’ll leave it to both the President of the Commission and the British Prime Minister to announce whatever has to be announced this afternoon, but I think it’s clear that very significant progress has been made,’ he told RTE Radio.

‘Over the last number of months, trust did build up between the two parties. Very substantial and serious negotiations have taken place in fairly significant detail, working up fairly substantive papers.’

Mr Martin said the customs data agreement struck earlier this year was a ‘gamechanger’ that ‘facilitated a new fresh approach to that issue’.

The foreign affairs minister said the primary concerns that have been articulated by unionism in particular – include the bureaucratic barriers to goods being sent from Great Britain to Northern Ireland, the ‘democratic deficit’ on what input Northern Ireland would have on any future EU regulations, and state aid issues – had been heard.

‘All of these issues, I think, have been responded to. I think the European Union has listened,’ he said.