The proposals that Sunak agreed with the European Commission president, Ursula von der Leyen, were passed by a large majority vote on the afternoon of Wednesday March 22 but 22 of his own MPs voted against the deal.

Among the Conservative rebels were Boris Johnson and Liz Truss, another former party leader, Iain Duncan Smith, and the former Cabinet ministers Jacob Rees-Mogg, Priti Patel and Simon Clarke.

The vote was passed by 515 votes to 29. A breakdown of the votes showed that six Democratic Unionist party (DUP) MPs opposed the location, along with the 22 Tories, plus former the Tory MP Andrew Bridgen, who has lost the whip.

The Democratic Unionist Party (DUP) had previously said before the count that it would vote against the plans and its leader, Sir Jeffrey Donaldson, said he would continue to work with the government on “outstanding issues”.

But what is in the deal and why it is so significant?

Why was the Northern Ireland Protocol a source of tension?

The protocol formed a key section of Boris Johnson’s Brexit deal. It was signed by the then-prime minister in 2020 and was designed to prevent a hard border on the island of Ireland.

To sustain the border free-flowing, London and Brussels essentially moved modern regulatory and customs checks required by Brexit to the Irish Sea.

The recede introduced red tape on trade between noteworthy Britain and Northern Ireland, creating a headache for many businesses and enraging loyalists and unionists who claim the region’s area within the UK has been undermined.

The row over the modern arrangements has left Northern Ireland without a functioning devolved government, after the Democratic Unionist Party used its veto to bring down the administration in protest at the protocol. Its boycott means a ministerial executive cannot function and the legislative assembly cannot conduct any business.

What is in the modern deal on trade?

The Windsor Framework, as the set of proposed arrangements is called, was announced by Mr Sunak and the European Commission president, Ursula von der Leyen, last month. The prime minister claimed that the agreement “removes any sense of a border in the Irish Sea”.

The deal, which took months of negotiations, covers a range of areas including trade, VAT regulation and the role of Stormont in EU laws that apply to Northern Ireland.

At the core is the creation of a modern system for the flow of goods. Anything destined for Northern Ireland will travel there as section of a “green lane”, with significantly fewer checks. Anything that could cross the border and enter the EU’s single market will travel through a separate “red lane”.

The Government said the green lane would be accessible to the broadest range of traders across the UK, including small businesses wanting to bring goods into Northern Ireland.

The changes should also benefit food retailers, addressing many of the vocal concerns about the difficulties of moving British sausages and other foodstuffs into Northern Ireland as section of protocol rules on agri-food.

“If food is available on supermarket shelves in noteworthy Britain, then it will be available on supermarket shelves in Northern Ireland,” Mr Sunak said at a recent press conference.

Supermarkets, wholesalers and hospitality companies would all able to use the modern green lane. The requirement for health certificates for individual food products would be removed and “radically reduced checks” on foodstuffs are promised.

Customs processes for parcels would be scrapped, which would mean that parcels can be sent between people in noteworthy Britain and Northern Ireland without any additional requirements.

Travellers with pets acquire also been assured that, under the agreement, they would be able to travel throughout the UK without the requirement of extra health treatments, modern costs or extra documents.

The issue is a concern for many, with the protocol creating a range of modern rules for cats and dogs moving from noteworthy Britain to Northern Ireland – including the requirement of an animal health certificate and a rabies vaccination.

As section of the deal, the legal text of the protocol has been amended on VAT. Under current arrangements, EU VAT and excise rules for goods generally apply in Northern Ireland.

Mr Sunak has said that under his deal this will change, and the legal text of the protocol would be amended to allow the UK Government to “fabricate critical VAT and excise changes for the whole of the UK”.

Alcohol duty, for instance, was mentioned – with Mr Sunak suggesting that the cost of a pint in the pub could be cleave for Northern Irish drinkers.

The Windsor Framework also lifts the ban on seed potatoes moving from noteworthy Britain to Northern Ireland.

What is the role of the European Court of Justice under the agreement?

It had been expected that both the UK and the EU would try to find a way around the difficult role of the European Court of Justice (ECJ). Concerns about the oversight role of the court acquire been raised by the DUP and some Tory backbenchers, with the issue less about trade and more about sovereignty.

The ECJ is the final arbitrator of EU law issues in the region, given that Northern Ireland essentially remains within the single market for goods.

The Government believes that the agreement significantly narrows the role of the ECJ, with a modern approach set to address some of the concerns of a democratic deficit for Northern Irish representatives in the application of EU law.

That arrangement, dubbed the Stormont brake, is described in the agreement as giving Stormont a “genuine and powerful role” in deciding whether significant modern rules on goods that affect life in the region would apply. It is set to function along the same lines as the qualified Friday Agreement safeguard of the petition of concern.

Under that Stormont arrangement, 30 MLA signatures are needed to secure a valid petition, which then triggers a vote that requires a majority of both nationalist and unionist MLAs to pass.

It remains to be seen how the arrangement will be introduced into the Stormont institutions, if power sharing does return but Downing Street has been clear that once triggered the brake will give the Government the power subject to qualifying criteria to veto any modern or amended EU rule.

But speaking to reporters, Ms von der Leyen said the ECJ is the “sole and ultimate arbiter of EU law” and will acquire the “final say” on single market decisions.

She described the Stormont brake as something that would be an emergency mechanism that would hopefully not be needed.

What does the EU consider of the modern deal?

Ms von der Leyen spoke highly of the efforts to reach a deal, calling it “historic” and one that opened a “modern chapter” in UK-EU relations.

In Dublin, Taoiseach Leo Varadkar said that the EU had moved “a lot” to facilitate a deal.

“It’s a uniquely positive arrangement for Northern Ireland businesses in particular that trade can flow freely back and forth from Britain to Northern Ireland, without any need for any checks or complications, provided those goods stay in Northern Ireland,” he said.

When would the changes grasp effect?

The prime minister said that the modern agreement would fabricate a inequity “almost immediately” but it does seem that at least some of the changes would advance into effect at various times. For instance, modern arrangements for post and parcels would grasp effect from September 2024 – while some of the exact details of the implementation of the Stormont brake are still to be worked out.

But Downing Street has been clear that significant parts of the deal can be introduced even without Stormont returning immediately.

What happens to the Northern Ireland Protocol Bill?

Boris Johnson’s controversial legislation to override post-Brexit rules on Northern Ireland has been jettisoned by the prime minister. Brussels has agreed in turn that it will scrap its legal action against the UK, launched in retaliation over the former prime minister’s Northern Ireland Protocol Bill.

Downing Street believes that the modern agreement means there is no longer legal justification for the bill, which is currently in the Lords and was still being championed by Mr Johnson only last week.