LONDON — Prime Minister Boris Johnson is facing mounting pressure for his plans to override the UK's Brexit deal with the EU after two of his predecessors came together to speak out against the move.

Former British Labour leader Tony Blair and Conservative Sir John Major implored lawmakers to reject new legislation proposed by Johnson, as it threatens the peace process in Ireland, trade negotiations, as well as the integrity of Britain.

"We both opposed Brexit. We both accept it is now happening. But this way of negotiating, with reason cast aside in pursuit of ideology and cavalier bombast posing as serious diplomacy, is irresponsible, wrong in principle and dangerous in practice," they said in the Sunday Times.

"It raises questions that go far beyond the impact on Ireland, the peace process and negotiations for a trade deal — crucial though they are. It questions the very integrity of our nation."

It came after Johnson said the controversial bill, which would directly violate the Brexit deal it signed with the European Union last year, is necessary to stop the bloc's threats of installing a "blockade" in the Irish Sea.

"We cannot leave the theoretical power to carve up our country — to divide it — in the hands of an international organization," he wrote in the Telegraph newspaper. "We have to protect the UK from that disaster, and that is why we have devised a legal safety net."

Johnson faced a rebellion from within his party with Conservative rebels coming together to undermine the legislation.

Former minister, Bob Neill, tabled an amendment the bill with the aim of creating a parliamentary veto on overriding the UK's Brexit deal with the Brussels, which will see a faceoff at the bill’s second reading in the House of Commons next week.

The move is backed by the likes of former immigration minister Damian Green and the ex-minister and solicitor general Oliver Heald, as well as Simon Hoare, chair of the Northern Ireland Affairs Select Committee.

But Johnson has said if Conservative lawmakers block the internal market bill by rebelling, the EU could "carve up our country" and "seriously endanger peace and stability" in Northern Ireland.

“We are now hearing that unless we agree to the EU’s terms, the EU will use an extreme interpretation of the Northern Ireland protocol to impose a full-scale trade border down the Irish Sea," the prime minister wrote.

“We are being told that the EU will not only impose tariffs on goods moving from Great Britain to Northern Ireland, but that they might actually stop the transport of food products from great Britain to Northern Ireland.

“I have to say that we never seriously believed that the EU would be willing to use a treaty, negotiated in good faith, to blockade one part of the UK, to cut it off; or that they would actually threaten to destroy the economic and territorial integrity of the UK.”

However, both the EU and Ireland have cautioned that Johnson’s bill is more of a threat to the Good Friday Agreement than a protective measure.

European Parliament chiefs have said that they would “under no circumstances ratify” a trade deal if “UK authorities breach or threaten to breach” the Withdrawal Agreement.

Johnson's bill gives other ministers powers to "disapply" parts of the rules agreed in October 2019 for goods that cross in and out of Northern Ireland.

EU leaders warned that these rules, formally known as the Northern Ireland Protocol, are legally binding and breaking them would be a breach of international law.

Brandon Lewis, the British minister responsible for Northern Ireland, insisted the new UK bill would break international law in a "very specific and limited way". — Euronews