LONDON — Britain moved ahead on Monday with plans to scuttle the post-Brexit trade rules in Northern Ireland, risking a clash with the European Union, a rift with neighboring Ireland, and tensions with the United States.
But the long-anticipated legislation may be most revealing for what it says about the altered political landscape since Prime Minister Boris Johnson survived a no-confidence vote in his Conservative Party last week.
Mr. Johnson faces a tricky path navigating the bill through a Parliament emboldened by the revolt against him. Some of the Tory rebels are expected to oppose the legislation on the grounds that it violates international law. It would unilaterally eliminate border checks on goods flowing from mainland Britain to Northern Ireland.
The prime minister accepted a more aggressive approach pushed by his foreign secretary, Liz Truss. She, analysts say, is burnishing her own credentials with hard-line Brexiteers in the party for a possible future leadership challenge against him, and Mr. Johnson can ill afford to further antagonize his right-wing flank.
For a dispute that has such wide-ranging international repercussions for Britain, it is remarkable how much it has been colored by domestic politics. But successive British governments have long viewed Northern Ireland through primarily a domestic lens, and none more so than Mr. Johnson’s.
“It’s all about this fight inside the Tory Party,” said Jonathan Powell, who served as chief of staff to Tony Blair, the former prime minister, and worked extensively on Northern Ireland. “They’re putting the interests of one man ahead of the interests of peace in Northern Ireland, and the interests of our relations with the E.U. and the U.S.”
British officials argue that the legislation is urgently needed to fix the trade disruption and political paralysis that resulted from its agreement with Brussels on Northern Ireland, which is a member of the United Kingdom but shares an open border with neighboring Ireland, a member of the European Union.
To keep that border open, Mr. Johnson had accepted checks on goods flowing from mainland Britain to Northern Ireland. But the arrangement, known as the Northern Ireland Protocol, alienated the main pro-unionist party in the North, which has refused to take part in a power-sharing government until Britain overhauls it.
Under the legislation published by government on Monday, goods would be divided into green and red lanes. Those bound for Northern Ireland from Britain would no longer undergo checks, while those bound for the Irish Republic would be in the red lane and would continue to be subject to checks.
The legislation would also no longer recognize the authority of the European Court of Justice to settle disputes, a prime bone of contention in months of fruitless negotiations between London and Brussels to revamp the protocol.
Having failed to work out a compromise, Britain is essentially saying it will no longer abide by the agreement. Its unilateral approach was condemned by the European Commission and the Irish government and has drawn warnings from the Biden administration. The United States fears it could jeopardize the Good Friday Agreement, which ended decades of sectarian violence in Northern Ireland.
Nor is it clear that it will end the political paralysis in the North. Lawmakers for the Democratic Unionist Party said they would wait to see how the bill was implemented before deciding whether to rejoin the power-sharing government there.
“Unilateral action is damaging to mutual trust,” Maros Sefcovic, a vice president of the European Commission, who has led negotiations with Britain on the protocol, said in a statement. Brussels, he said, would consider resuming legal action against Britain that it had put on hold during the negotiations.
Mr. Johnson denied that the legislation violated international law, arguing that, far from undermining the Good Friday agreement, Britain was meeting its higher legal obligation of preserving the accord. British officials also invoked the doctrine of necessity, a principle in international law that allows a state to temporarily disregard its obligations if it is facing a “grave and imminent peril.”
And yet, for all the claims of a brewing crisis in the North, Mr. Johnson also tried to play down the real-world significance of the legislation.
“It’s a bureaucratic change that needs to be made,” he said in an interview with LBC, a British radio broadcaster, before Ms. Truss presented the bill. “Frankly, it’s a relatively trivial set of adjustments in the grand scheme of things.”
Legal experts noted that the legislation would give the government the power to overturn all but three of the 19 provisions in the trade agreement, which was painstakingly negotiated with the European Union.
“That seems to me to be more than trivial,” said Catherine Barnard, an expert on European Union law at Cambridge University. “There is real concern about the fact that the U.K. appears to be trying to dismantle its commitments under the protocol.”
Few mainstream lawyers or legal scholars, she added, have argued that Britain’s move is not a violation of international law.
While Britain’s tactics have angered the European Union, officials in Brussels have been loath to allow the dispute to escalate into a full-blown trade war. Partly, that reflects a recognition that the legislation will take a year, or more, to take effect. Even if it passes the House of Commons, the House of Lords is likely to amend it in ways that may water down some of its effect. Partly, it reflects a desire by Brussels not to fracture the Western alliance in defense of Ukraine over an unrelated issue.
As foreign secretary, Ms. Truss has been deeply involved in forging that alliance. The fact that she is also the person most visibly pushing the legislation on Northern Ireland, analysts said, illustrates the political advantage that she believes can be extracted from taking a hard line toward Brussels on the protocol.
By hardening the legislation, particularly on issues like the European court, Ms. Truss could win the loyalty of the European Research Group, a group of fervently pro-Brexit lawmakers. Several of those lawmakers broke publicly with Mr. Johnson after the scandal over illicit parties held in Downing Street during the pandemic.
While Mr. Johnson’s victory in the no-confidence vote means he is probably safe for now, the prospect of further electoral setbacks, as well as a drumbeat of miserable economic news, suggests he could face another leadership challenge in the coming months. Ms. Truss leads most lists of potential rivals.
“This is the result of an acute political calculation on her part,” said Mujtaba Rahman, an analyst at the political risk consultancy, Eurasia Group. “Otherwise, there are pretty big downsides to what the government is doing.”