Tony Blair and John Major, two former prime ministers, have urged MPs to oppose the UK government’s “shocking” attempt to override parts of the Brexit withdrawal agreement.
Mr Blair and Sir John, former Labour and Conservative leaders respectively, said the proposal to renege on parts of last year’s Brexit divorce deal threatened “the very integrity of our nation”.
The internal markets bill — which will be debated in the House of Commons from Monday — includes clauses which override the Northern Ireland protocol, the part of the withdrawal agreement designed to prevent a hard border returning to the island of Ireland.
Boris Johnson, the UK prime minister, said the clauses were necessary to prevent Brussels from imposing a “full-scale trade border down the Irish Sea”.
But his actions have prompted a chorus of anger from an unlikely coalition of opposition leaders, former Tory leaders — including Eurosceptic Michael Howard — and overseas premiers.
The legislation would give ministers powers to modify or disapply rules relating to state aid and to the movement of goods between Britain and Northern Ireland if there was no UK-EU trade deal by January 1.
The government is braced for a rebellion by a significant handful of backbench Tory MPs and stormy sessions in the House of Lords later in the month.
Mr Blair and Sir John accused the government of “embarrassing the UK” with legislation that was “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 wrote in a joint article in the Sunday Times.
The former leaders — who have previously clashed with Mr Johnson over Brexit as former Remainers — said that respecting treaty obligations was “just as important” as domestic law.
Robert Buckland, justice secretary, argued on Sunday that the government was still “absolutely committed to the rule of law” and had drawn up the provisions in the legislation as a fallback in the event that no EU trade deal was struck.
“We are talking about a difference between international law and domestic law on a political scale,” he told Sky News. “It’s a world away, I would suggest, from issues of enforcement of the law and regulations on a day-to-day basis.”
Mr Buckland said the situation was “not at that stage” where he would consider resignation, arguing that the plan would hopefully never be used: “It’s a ‘break the glass in emergency’ provision if we need it,” he told the BBC.
Michel Barnier, the EU’s chief negotiator, meanwhile dismissed claims by Mr Johnson that the protocol on Northern Ireland was a threat to the integrity of the UK.
“We agreed this delicate compromise with Boris Johnson and his government in order to protect peace and stability on the island of Ireland,” he said. “We could not have been clearer about the consequences of Brexit.”
Mr Barnier separately denied that the EU was threatening to withhold “third-country” status from the UK to make it harder for food deliveries from Great Britain to Northern Ireland.
“The EU is not refusing to list the UK as a third country for food imports,” he said on Twitter. “To be listed, we need to know in full what a country’s rules are, including for imports. The same objective process applies to all listed countries.”