There are growing fears that a trade war with the EU is on the horizon after the UK government announced its plans to unilaterally change the Northern Ireland protocol.
The PM confirmed plans to bulldoze the agreement on Monday as the UK and EU remained at odds over the trading and checking of goods going in and out of Northern Ireland.
After 18 months of attempts to renegotiate, no mutually acceptable arrangement has been reached.
The EU says it will not renegotiate because the prime minister agreed to the terms when he signed the Brexit deal in January 2020.
The bloc has warned of "serious consequences" if the UK does back out of the arrangement, and launched legal action on Wednesday.
What is the Northern Ireland protocol?
The Northern Ireland protocol is a trade agreement that formed part of the Brexit deal.
The EU and the UK agreed inspections for goods would happen at ports in Northern Ireland – avoiding the need for a hard border with Ireland. Northern Ireland would also follow EU rules on product standards.
Goods checked at Northern Irish ports could then move into Ireland and the rest of EU.
The issue of the Ireland-Northern Ireland border became a major sticking point during Brexit negotiations.
Northern Ireland is the only part of the UK that shares a land border with the EU. Plus, the border is politically fragile due to the unrest and violence seen during the Troubles.
Any changes to the relationship between Ireland and Northern Ireland could risk the 1998 Good Friday Agreement and jeopardise peace.
While the republican party Sinn Fein has accepted the Brexit arrangement, unionist parties are frustrated with the agreement and have refused to form the Northern Irish assembly, saying the deal cuts off Northern Ireland from the rest of the UK.
This increasing unhappiness with the arrangement has been a driving factor for the government's decision to move away from its agreed deal. Among the proposed changes are:
Customs 'green channel': Exports passing from Great Britain destined for Northern Ireland will not need paperwork, checks or duties.
Customs 'red channel': Exports going from Great Britain destined for the Republic of Ireland or the rest of the EU by traders not in the "trusted trader scheme" will be subject to full checks and full customs procedures.
A 'dual regulatory system': Businesses can choose to operate under UK or EU law.
What is a trade war?
Often trade wars involve governments putting up tariffs or increasing restrictions on imports from a certain country, largely in retaliation for behaviour they don't like or agree with.
Trade wars can drive up prices and increase inflation, as well as damaging diplomatic relations.
There can be positive consequences for domestic growth, making production of certain goods cheaper than importing them from abroad.
In this instance, there are concerns that the EU could slap tariffs on exports on key British exports like salmon in retaliation for breaking the Brexit agreement, which would increase the price of the goods for businesses and consumers.
This, in turn, could result in the UK placing tariffs on EU goods arriving in the UK, driving up prices at the till.
How likely is a trade war?
A trade war is not an appealing avenue for either side given the deepening cost-of-living crisis on both sides of the Channel.
On Monday, the prime minister warned that a trade war over changes to the Northern Ireland protocol would be a “gross overreaction” by Brussels.
“All we are trying to do is simplify things, actually, to remove the barriers to trade between Great Britain and Northern Ireland,” he told LBC Radio on Monday.
However, there seems to be signs that preparations are already underway should the EU decide to retaliate.
On Tuesday, the BBC reported that companies like the German car manufacturer Volkswagen are preparing for that eventuality.
"There's a lot of communication going on. And there's also a dependency," Herbert Deiss, the chief executive of the company, told the broadcaster.
"We have a British brand, Bentley, which is doing extremely well… also the UK is our biggest export market in Europe for the premium brands for VW and Audi ... so I think there will be, let's say, a mutual interest now to keep [trade] open."
And in May, taoiseach Micheál Martin, the Irish prime minister, indicated a trade war was not off the table if the UK breached the Brexit deal it signed.
“It's very clear that everything's on the table in terms of any responses to what might happen," said Martin.
Shadow foreign secretary David Lammy has criticised the government's management of the issue.
"By tearing up the protocol it negotiated just a couple of years ago, the government will damage Britain’s reputation and make finding a lasting solution more difficult," said Lammy.
"The EU must show more flexibility as Labour has said from the start. But this legislation is not the way to unlock progress."
Watch: Boris Johnson faces EU legal row after plan to rewrite Northern Ireland’s Brexit deal