Former UK Prime Ministers Tony Blair and John Major have urged MPs to reject incumbent premier Boris Johnson's "shameful" attempt to override parts of the Brexit Withdrawal Agreement, it was reported on Sunday.

The Internal Market Bill, which will be formally debated in the House of Commons for the first time on Monday, addresses the Northern Ireland Protocol - the part of the Brexit Withdrawal Agreement designed to prevent a hard border returning to the island of Ireland, the BBC reported.

If it becomes a law it would give UK ministers powers to modify or "disapply" rules relating to the movement of goods between Britain and Northern Ireland that will come into force from January 1, if the UK and European Union (EU) are unable to strike a trade deal.

The EU has warned the UK it could face legal action if it does not ditch controversial elements of the Internal Market Bill by the end of the month.

But the government has argued that the measures in the bill were needed to protect the integrity of the UK and the peace process in Northern Ireland.

Writing in the Sunday Times, Major and Blair said the Johnson-led government's actions were "irresponsible, wrong in principle and dangerous in practice".

"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," they said.

The former leaders, both vehement opponents of Brexit, said that respecting treaty obligations was "just as important" as domestic law, and called for MPs to reject the legislation.

"As the world looks on aghast at the UK - the word of which was once accepted as inviolable - this government's action is shaming itself and embarrassing our nation," BBC quoted the former Prime Ministers as saying.

On Friday, Johnson urged Conservative MPs to back the bill during a Zoom call, while Cabinet Office minister Michael Gove insisted that the proposals were a means of protecting the "integrity" of the UK.

But opposition Labour Party leader Keir Starmer has accused Johnson of "reigniting old rows" by working to override his own Withdrawal Agreement.