British Brexit negotiator David Frost (center) arrives for negotiations with EU representatives at EU headquarters, in Brussels on Monday. The EU and Britain launched an intense five weeks of negotiations on a deal to define their post-Brexit relations. (Photo: AFP)

The European Union (EU) on Sunday rejected an incendiary claim by British Prime Minister Boris Johnson that the bloc is plotting to destabilize the UK as another week of Brexit high drama beckoned, headlined by a stormy parliamentary debate in London.

The war of words escalated over a new British government bill that London admits is in violation of its EU divorce treaty - legislation that has sparked a furious response from British former prime ministers Tony Blair and John Major.

Johnson's claim that the 27-nation EU is plotting to choke off food supplies via crippling new trade barriers between Britain and Northern Ireland is "spin and not the truth," Irish Foreign Minister Simon Coveney told BBC television.

Charles Michel, who heads the EU Council of government chiefs, said Britain's "international credibility" was at stake as both sides battle to unwind nearly 50 years of economic integration, following a deeply divisive referendum in the UK.

EU trade negotiator Michel Barnier insisted that a Northern Irish protocol in the EU treaty "is not a threat to the integrity of the UK," as claimed by Johnson in Saturday's Daily Telegraph newspaper.

Major and Blair, who led Britain through Northern Ireland's historic peace talks in the 1990s, wrote in the Sunday Times that the government's actions were "shaming itself and embarrassing our nation."

Backed by the EU, Ireland stresses the provisions for Northern Ireland were agreed by both sides to ensure fair competition after Brexit, and to comply with a 1998 peace pact that ended three decades of unrest in the province.

Johnson had accused the EU of threatening to tear the UK apart by imposing a food "blockade" between Britain and Northern Ireland, which is meant to enjoy a special status with the EU after Brexit.

Johnson said the EU's stance justified his government's introduction of the new legislation to regulate the UK's internal market and maintain access to Northern Ireland, after a post-Brexit transition period expires at the end of 2020.

The food dispute centers on the EU's reluctance to grant Britain "third country" status, which acknowledges that nations meet basic requirements to export their foodstuffs to Europe.

The EU is worried that post-Brexit Britain could undercut its own food standards, as well as rules on state aid for companies, and infiltrate its single market via Northern Ireland.

After the latest round of trade talks last week in London, Barnier had said "many uncertainties" remained about Britain's food export regime after January 1, and "more clarity" was needed for the UK to enjoy third-country listing.