The development has prompted fury in Dublin, Brussels and other EU capitals and it is still far from clear that the legislation which had its first reading in the House of Commons this evening will ever make it on to the statute book.
If that does happen, it could be a year away – meaning that there is no immediate solution to the practical problems arising from the Irish Sea border.
The bill seeks to hand the UK powers to unilaterally rewrite the bulk of the Northern Ireland Protocol, which kept the region in the EU single market after Brexit, creating a customs border with Great Britain.
If passed, the new law would allow ministers to rip up the regulatory framework both sides agreed to in 2019 and replace it with new rules on customs checks, tax and arbitration.
"This is a reasonable, practical solution to the problems facing Northern Ireland," Foreign Secretary Liz Truss said in a statement. "It will safeguard the EU Single Market and ensure there is no hard border on the island of Ireland."
She said that Britain is "completely serious" about passing legislation on Northern Ireland that will change the way the Brexit deal agreed with the European Union is applied.
"We're completely serious about this legislation," she told reporters when asked if the plan was just a negotiating tactic.
"It does fix the problems in the Northern Ireland Protocol. It also protects the EU single market so the EU are no worse off as a result of this legislation," she said in a video statement that coincided with the publication of legislation.
She said Britain remained open to negotiations with the EU and that the British government was acting within international law.
Asked about comments from Taoiseach Micheál Martin, who earlier warned that a unilateral breach of the Brexit deal would be very serious, Ms Truss said:
"I would strongly encourage the Irish Taoiseach to... discuss this with the EU to get a change in the mandate and then we can go to the negotiating table."
At the heart of the new plan is a new “green and red lane approach backed by commercial data and a trusted trader scheme” – with the green lane for goods staying in NI and the red lane for items at risk of going on to the Republic or for traders not in the trusted trader scheme.
Non-commercial goods such as post and parcels would automatically go through the green lane. Strong penalties would be used to discourage abuse of the green lane, with a UK government briefing saying: “Traders who abuse the new system will face robust penalties, including civil and criminal charges, and would not be able to use the green lane in the event of non-compliance.”
The UK government said this approach would mean that “goods staying in the UK would be freed of unnecessary paperwork, checks and duties, with only ordinary commercial information required rather than customs processes or complex certification requirements for agrifood products”.
The bill would allow for “a dual-regulatory regime that gives choice to NI business… goods can be placed on the market in NI if they meet either UK rules, EU rules, or both – ensuring that consumers can access the products they want, and avoiding gaps on supermarket shelves.”
DUP leader Jeffrey Donaldson welcomed the British government’s move, saying that it was long overdue.
But EU vice president Maros Sefcovic said that the EU would consider restarting the legal action it began last year over past unilateral grace periods which the UK government put in place, and consider fresh legal action.
He said that the EU will not renegotiate the Northern Ireland Protocol agreement.
"Renegotiating the protocol is unrealistic... Any renegotiation would simply bring further legal uncertainty for people and businesses in Northern Ireland. For these reasons, the European Union will not renegotiate the protocol," Mr Sefcovic said in a statement.
Earlier, Foreign Affairs Minister Simon Coveney warned that Britain had potentially collapsed the post-Brexit trade deal it agreed with the EU by publishing legislation that overrides the agreement.
However, Mr Coveney insisted UK prime minister Boris Johnson’s legislation aimed at circumventing the Northern Ireland Protocol will not result in a border on the Island of Ireland.
The minister also compared Mr Johnson’s decision to break an international treaty to Russian president Vladimir Putin’s invasion of Ukraine.
Speaking outside Government Buildings, Mr Coveney said there is “absolute solidarity” across the European Union to ensure Ireland does not become “collateral damage for the irresponsible actions of the British government”.
“We aren't predicting border infrastructure on the island of Ireland,” he said.
“Instead, the EU is going to have to respond and to hold the British government to account for breaching its word and breaching international agreements that have ensured that more infrastructure wouldn't be required,” he added.
Mr Coveney said Brexit had caused a “huge amount of stress and strain” for border communities and said the protocol, which was agreed by the British government, was the solution to ensuring there would be no need for border checks.
The minister said he hoped Britain’s actions would not spark a trade war but insisted the EU will not accept the approach taken by Mr Johnson’s government.
“The last thing we want is tension and friction with the British government at the moment given all of the other challenges that we all collectively face together but unfortunately British action is forcing us into this position that we don't want to be in,” he said.
Mr Coveney said the move was “damaging Britain's international reputation in a significant way” at a time when the EU is trying to hold Russia to account for its “aggression in Ukraine by using international law”.
“We see a British government now deliberately moving in a direction to undermine its own credibility by breaking international law as well and that's something we've warned against. We've pleaded with the British government not to do this, but they've moved ahead anyway, for their own reasons,” he added.
Sinn Féin's Stormont leader Michelle O'Neill said Mr Johnson's plan to amend the Northern Ireland Protocol was "reckless and disgraceful" and would jeopardise jobs.
Speaking to the media at Stormont, Ms O'Neill said: “Today's action by Boris Johnson in Westminster is absolutely reckless, it is disgraceful, it does nothing to serve the interests of the people here.
“It flies in the face of an international agreement which he himself negotiated. It is in clear breach of international law."
She added: “The reality is that the protocol is working. Clearly, what we want here is certainty and stability.
“We are 40 days out from the election and yet we don't have an Executive formed because the DUP are blocking the formation of an Executive.
“I don't think that is acceptable to the public while they are dealing with a cost-of-living crisis."
Meanwhile the Taoiseach urged the British government to re-engage with the EU over the Northern Ireland Protocol and not to press ahead with unilateral action to allow sections of the international agreement be overridden.
As the UK prepared to unveil legislation in parliament to change the post-Brexit trade agreement, Mr Martin, speaking in Cork, said both Dublin and Brussels wanted to have meaningful negotiations with London over the substantive issues involved.
"I would say to the British government (that they) should enter into those discussions and negotiations now," he said.
"Unilateralism does not work – unilateralism has never worked in the context of the Good Friday Agreement. I am still very concerned that we are witnessing a denial of democracy.
"We have had (a Northern Ireland) Assembly election and yet we do not have an Assembly convened. The people's voice needs to be reflected in the institutions being put in place, the Assembly and the (Northern Ireland) Executive.
"Europe has been flexible, Europe wants to find a resolution to these issues.
“(The) European (Union) has met the enterprise and business interests in Northern Ireland. I have personally met with them recently.
“The British government needs to engage with the business interests in Northern Ireland and with industry in Northern Ireland.”
Mr Martin said he believed unilateral action would ultimately benefit no one in the long-term – and he said there were serious concerns about the impact it would have on trust and co-operation between various parties over Northern Ireland.
“The British government has a tendency to ‘big up’ decisions like this and, once they announce them, try to trivialise them.
“Essentially announcing the unilateral breaching of an international agreement is pretty serious stuff.
“This is a very serious issue and it goes to the heart of the issue of trust. The EU needs to have a trusted partner to negotiate with.
“The next deal has to be one – if there is to be further negotiation on a deal – that will be adhered to. That is a fairly basic point that the British government needs to reflect on.”
The Taoiseach’s comments came after Foreign Affairs Minister Mr Coveney told his British counterpart Liz Truss the decision to introduce legislation to override the protocol “marks a particular low point in the UK’s approach to Brexit”.
In a phone call with the UK foreign secretary this morning, Mr Coveney insisted the legislation published today would breach the UK’s commitments under international law and was “deeply damaging to relationships” between Ireland and Britain.
Ms Truss called Mr Coveney to inform him of her intention to publish the legislation.
In a 12-minute telephone conversation, Mr Coveney reminded Ms Truss that the protocol was the negotiated solution and was ratified by Westminster to avoid a hard Brexit and was pursued by the UK government.
The minister said the UK’s unilateral approach is “not in the best interest of Northern Ireland and does not have the consent or support of the majority of people or business in Northern Ireland”.
“Far from fixing problems, this legislation will create a whole new set of uncertainties and damage relationships,” the Department of Foreign Affairs said in a statement.
The Government is planning a robust response to British prime minister Mr Johnson introducing legislation in the House of Commons that will override the Northern Ireland Protocol.
Brexit trade talks are set to become even more tense from today, with the publication of draft British laws which it is believed will breach international law.
Today, ahead of the publication of the legislation, Mr Johnson insisted the plan to effectively override parts of the Brexit deal with Brussels was "not a big deal" as he was warned the move would "deeply damage" relations with the EU and Ireland.
Mr Johnson insisted the legislation would introduce "relatively simple" bureaucratic changes and warned it would be a "gross overreaction" if Brussels were to seek to retaliate by triggering a trade war.
Mr Johnson told LBC Radio: “What we have to respect – this is the crucial thing – is the balance and the symmetry of the Belfast/Good Friday Agreement.
“We have to understand there are two traditions in Northern Ireland, broadly two ways of looking at the border issues. One community at the moment feels very, very estranged from the way things are operating and very alienated.
“We have just got to fix that. It is relatively simple to do it, it's a bureaucratic change that needs to be made.
“Frankly, it's a relatively trivial set of adjustments in the grand scheme of things.”
Mr Johnson disagreed with claims that the move breaks international law, arguing that "our higher and prior legal commitment as a country is the Belfast/Good Friday Agreement and to the balance and stability of that agreement".
The legislation is expected to face opposition in the House of Commons – including from some within the Tory ranks – and ministers will face an even tougher battle in the House of Lords.
Financial Times reported that an internal note had been circulating among Tories opposed to the bill, which said: "Breaking international law to rip up the prime minister's own treaty is damaging to everything the UK and Conservatives stand for."
Irish ministers have ratcheted up their rhetoric around Mr Johnson’s protocol plans, as Northern Ireland Secretary Brandon Lewis insisted the new legislation will not breach the agreement struck between the EU and UK.
However, the Government is expecting the worst and planned to hit back at Britain once the controversial bill is unveiled.
“We’ll want the EU to wade in, but if the legislation is as brazen as they are previewing we will have to come out strong,” a senior Government source said.
Another senior Irish Government figure said the situation has become “very tenuous” due to ongoing Conservative Party leadership issues, which saw Mr Johnson face a motion of no confidence vote earlier this month.
“Northern Ireland is growing more than other parts of the UK so the rationale is not there for this legislation,” the source said.
A Cabinet minister said the Conservatives’ “obsession and division over Europe show no signs of abating,” adding this is “bad medicine”.
The comments came after Mr Coveney suggested British foreign secretary Ms Truss was using the protocol row to further her Conservative Party leadership ambitions.
Mr Coveney said relations between Ireland and Britain are “in a bad place” at present.
“It seems to us, looking from Dublin, that their only consideration is around leadership ambition and leadership survival within the Conservative Party,” the minister said in comments believed to be targeted at Ms Truss.
The Government believes Mr Johnson will struggle to get his protocol legislation through the House of Commons and the House of Lords.
Business Post reported that agri-food businesses have been told the bill will remove all customs checks for goods moving within the UK and will also allow firms to choose between applying EU or UK standards for their products.
It will also remove any oversight of regulations from the European Courts.
Yesterday, Mr Lewis said the legislation will be “lawful” and “correct”.
He said he hoped the new laws will persuade the DUP to give their backing to the restoration of power sharing and return to Stormont.
“If the DUP are true to what they have said is the reason they withdrew the First Minister in the first place, around wanting to see positive progress on fixing the problems of the protocol, this legislation will do that and I hope they will respect that and deliver on that.”
However, Sinn Féin leader Mary Lou McDonald said Mr Lewis was “talking through his hat”.
“What the Tory government is proposing to do in breaching international law is to create huge damage to the Northern economy, to the Irish economy,” she said.
“They propose to breach international law and are on an agenda of undermining, attacking and damaging the Good Friday Agreement.”
The UK Labour Party’s shadow chancellor, Rachel Reeves, said the Conservative Party had developed “a record for law-breaking”.