LONDON (BLOOMBERG) - British Prime Minister Boris Johnson is heading for a fresh fight with his own Conservative Party over a plan to override the Brexit deal with the European Union (EU), which risks a trade war with the bloc and renewed legal retaliation.

Mr Johnson's plan published Monday (June 13), which would give ministers the power to unilaterally rewrite the bulk of the Northern Ireland protocol, was immediately condemned by the EU, panned by legal experts and may face stiff opposition in Parliament.

In a sign of the trouble to come, Conservative Member of Parliament (MP) Roger Gale, a long-standing Johnson critic, said he intended to vote against it.

"I do not see how I or indeed any Member of Parliament can vote for a breach of international law," Mr Gale said in a statement to Bloomberg News.

The government's plan overrides a treaty "freely entered into and signed by the Prime Minister," Mr Gale said.

He was among 32 Tory MPs who did not support a previous attempt by Mr Johnson in 2020 to unilaterally amend the post-Brexit settlement in Northern Ireland, when his government said it planned to break international law in a "limited and specific" way.

At that time, 30 of the MPs abstained, and two voted against, including Mr Gale. Mr Johnson eventually dropped that proposal after further talks with the EU.

Mr Stephen Hammond, a Conservative MP who abstained in the 2020 vote, also expressed reservations about the government's approach.

"Many colleagues are very concerned that this Bill will breach international law and the commitments we have freely entered into," he said in a statement.

"There is frustration about why now and how we are proceeding."

Mr Johnson's new Bill is likely to run into trouble in Parliament's unelected Upper Chamber - the House of Lords - where peers have repeatedly pushed back on efforts to override the Brexit agreement.

Lord Pannick QC, who acted for SCM Private LLP co-founder Gina Miller in the high-profile Supreme Court case which ruled that Mr Johnson unlawfully prorogued Parliament in 2019, said the prime minister's plan is "plainly in breach of international law".

"I would be very surprised if the government were able to obtain the approval of the House of Lords for this Bill," Lord Pannick, who is a crossbench peer, said in a statement.

The brewing political opposition comes at a dangerous moment for Mr Johnson, who last week saw more than 40 per cent of his MPs vote against him in a confidence ballot. The parliamentary pushback also means it could be at least a year before his plan passes into law, during which time he still wants to pursue a negotiated settlement with the EU.

Mr Johnson says the plan is necessary to remove cumbersome bureaucracy on trade between Northern Ireland and the rest of Britain, which is a function of the Brexit deal he agreed to in 2019. Mr Johnson agreed to a de facto customs border in the Irish Sea after Brexit to avoid the need for a hard border on the island of Ireland.

Defending the government's approach on Monday, Foreign Secretary Liz Truss said the plan is a "reasonable, practical solution to the problems facing Northern Ireland".

The government's statement of its legal position said overriding the Brexit deal is necessary to protect the 1998 Good Friday peace deal.

Yet legal experts questioned that analysis. Mr Jonathan Jones, a consultant at Linklaters who resigned as the government's most senior lawyer in 2020 over the UK's then plans to alter the protocol, told Sky News that the government's legal position, is "very thin and unpersuasive".

The bill "neutralises" large parts of the agreement "and gives ministers powers to turn off yet more, almost all of the protocol", he said.

And the EU's chief Brexit negotiator, Maros Sefcovic said the bloc will now consider legal proceedings against Britain.

"Unilateral action is damaging to mutual trust," Mr Sefcovic said. The bloc's reaction will be "proportionate," including considering both continuing infringement proceedings that were put on hold last year and opening fresh legal procedures that "protect the EU Single Market from the risks that the violation of the protocol creates for EU businesses and for the health and safety of EU citizens", he said.

Infringement proceedings by the EU have been suspended during negotiations over how the protocol operates and if unfrozen could ultimately lead to financial penalties being imposed on Britain. Other options open to the EU include suspending its trade agreement with Britain, stopping the privileged access British companies have to the single market and halting talks over the status of Gibraltar, according to a person familiar with the matter.

Mr Johnson is also trying to restore the Northern Ireland executive, which has collapsed after the Democratic Unionist Party (DUP) refused to participate in protest at the protocol. DUP leader Jeffrey Donaldson said Britain's plan "has the potential to secure a permanent pragmatic solution", but he did not commit to returning to take part in the region's devolved government.