Boris Johnson has urged Conservative MPs to support Brexit-related legislation which his government has admitted breaks international law.
Addressing about 250 MPs on Friday evening, the prime minister said the controversial UK Internal Market Bill was necessary in order to avoid “an economic barrier down the Irish Sea”.
He added that certain clauses in it are “absolutely vital to protecting the integrity of our country”.
The bill overrides parts of the EU divorce deal, and has sparked fury in Brussels, which has threatened legal action over what it considers a violation of an international treaty.
The controversy deepened while the call with MPs was going on, with European Parliament leaders saying they would “under no circumstances ratify” any trade deal reached if “UK authorities breach or threaten to breach” the Withdrawal Agreement.
Speaking to Sky News, Minister for the Cabinet Office Michael Gove claimed the EU had not been “keeping to their side of the bargain” on the Brexit deal and insisted the government had been “operating within the rule of law”.
That came despite Northern Ireland Secretary Brandon Lewis admitting to MPs earlier this week that the proposed legislation “does break international law in a very specific and limited way“.
The bill was drawn up to ensure trade between all four home nations remains barrier-free after the Brexit transition period ends on 31 December 2020.
In his address, Mr Johnson said a gap had opened up between the UK and EU over Northern Ireland.
He told MPs: “In the last few weeks I’ve had a concern about a difference of opinion that is becoming stark in their interpretation and our interpretation of the Northern Ireland protocol.”
He continued: “The difficulty has been that the EU has decided that unless we agree to their interpretation of what the checks would be, then the default position in the event of there being no agreement is that there should be nothing short of an economic barrier down the Irish Sea with tariffs.”
The PM added: “So what we need to do is clear up what I think is a serious anomaly in the protocol and put a safety net under it.
“What we can’t have is the threat of a border down the Irish Sea and the threat of the breakup of the United Kingdom.”
Writing in The Daily Telegraph on Saturday, Mr Johnson said Brussels would use an “extreme interpretation” of the Northern Ireland Protocol to impose “a full-scale border down the Irish sea” that could “carve up our country” and “seriously endanger peace and stability” in 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,” he added.
“If we fail to pass this bill, or if we weaken its protections, then we will in fact reduce the chances of getting that Canada-style deal,” he wrote.
“Let’s remove this danger to the very fabric of the United Kingdom. Let’s make the EU take their threats off the table. And let’s get this bill through, back up our negotiators, and protect our country.”
Mr Johnson urged MPs to look at the bill carefully, asking them not to return to the “miserable, squabbling days of last autumn”.
It is understood there were connection issues and the prime minister did not take questions.
Some senior Conservatives are planning to amend the legislation, and grandees including former party leaders Michael Howard, John Major and Theresa May have spoken out against it.
Lord Howard described the government’s admission that the proposed legislation would break international law as a “very, very sad day”.
The European Commission has given the UK until the end of the month to drop it.
However, the prime minister’s official spokesman said the government’s position remained that provisions within the bill were “critical” to the preservation of the Northern Ireland peace process.
He said the UK would continue to strive for an agreement and called on the EU side to show “more realism”.
The bill returns to the Commons on Monday.