Cabinet Office minister Michael Gove has joined Boris Johnson in warning that Brussels could break up the UK if MPs do not approve controversial legislation to override parts of the Brexit deal.
Mr Gove echoed the Prime Minister on Saturday in declaring that the EU could put "at threat the integrity" of the Union, and insisted the Government could see off a Tory rebellion.
In incendiary remarks, Mr Johnson said Brussels was threatening to put a "blockade" in the Irish Sea which could "seriously endanger peace and stability" in Northern Ireland.
He was working to quell a plan to amend the legislation from senior Tories who are incensed that it could break international law by overriding the Withdrawal Agreement signed by Mr Johnson in October.
Pictures of the week: September 6 - 12
Pictures of the week: September 6 - 12
Naked activists holding placards during the Redress the Injustice Protest.
Extinction Rebellion Fashion Action (XRFA) demonstrate outside the Topshop and Topman store on Oxford Street, opposing the fashion industry�s many human, animal and environmental injustices claiming that, it currently produces around 10\% of global carbon emissions. Its emissions are predicted to increase by around 50\% by 2030. (Photo by Dave Rushen / SOPA Images/Sipa USA)
Artist Irek Jasutowicz works on a new mural of Leeds United soccer team manager Marcelo Bielsa near Hyde Park in Leeds, England Thursday Sept. 10, 2020. The West Yorkshire club will mark their return to the English Premier League after a 16-year wait with a trip to champions Liverpool on Saturday. (Danny Lawson/PA via AP)
EDITORIAL USE ONLY (Left to right) Fatima Bajwa and Jahanzeb Khan after tying the knot at the UK's first drive-through wedding service, launched by ride-hailing app, FREE NOW for couples whose own weddings have been postponed due to the COVID-19 pandemic, London.
Australia's captain Aaron Finch, left, and David Warner walk out to bat during the first ODI cricket match between England and Australia, at Old Trafford in Manchester, England, Friday, Sept. 11, 2020. (AP Photo/Jon Super, Pool)
LONDON UNITED KINGDOM - SEPTEMBER 11: People take part in a demonstration against Chinaâs persecution of Uighurs in Xinjiang in front of Chinese Embassy in London, United Kingdom on September 11, 2020. (Photo by Hasan Esen/Anadolu Agency via Getty Images)
A view of the scene after a bus crashed into a railway bridge on Well House Lane, in Winchester, England, Thursday, Sept. 10, 2020. At least three children were taken to hospital with serious injuries. (Andrew Matthews/PA via AP)
A woman wearing a face mask looks at her mobile phone. (Photo by Dinendra Haria / SOPA Images/Sipa USA)
Young people out in Newcastle city centre at night. People in England will be banned from meeting in groups of more than six from Monday as ministers try to tackle the rising number of coronavirus cases across the UK.
The statue of Winston Churchill in Parliament Square is seen with graffiti reading 'is a racist' on the plinth, in London, Thursday, Sept. 10, 2020.(AP Photo/Alberto Pezzali)
EU Chief negotiator Michel Barnier gestures as he leaves after a meeting at Westminster Conference Centre in London, Thursday, Sept. 10, 2020. UK and EU officials have their eighth round of Brexit negotiations in London. (AP Photo/Kirsty Wigglesworth)
A woman wearing a mask to protect against coronavirus, leaves a store, a day after the county borough of Caerphilly began a local lockdown following a "significant rise" in coronavirus cases, in Caerphilly, South Wales, Wednesday, Sept. 9, 2020. (Ben Birchall/PA via AP)
Police stopping a group of protesters in Whitehall near Downing Street joining other activists during the demonstration.
Extinction Rebellion protesters in Parliament Square try to stop British Prime Minister, Boris Johnson getting from Downing Street to Parliament by sitting in the road outside. The activists use nonviolent means to put pressure on politicians to implement actions to slow down climate change. (Photo by Dave Rushen / SOPA Images/Sipa USA)
Extinction Rebellion activists march along Parliament Street, as part of a climate change protest, in London, Tuesday, Sept. 8, 2020.(AP Photo/Alberto Pezzali)
LONDON, Sept. 8, 2020 -- A woman wearing a face shield walks past the London Eye in London, Britain, Sept. 8, 2020.
The latest British official figures showed Tuesday that COVID-19 death toll had hit 57,400 as British people are being urged to take the pandemic seriously or face "a bumpy road" ahead. (Photo by Han Yan/Xinhua via Getty) (Xinhua/Han Yan via Getty Images)
LONDON, Sept. 8, 2020 -- British Prime Minister Boris Johnson walks back to 10 Downing Street in London, Britain, Sept. 8, 2020.
Crucial talks aimed at finding a post-Brexit trade deal between Britain and the European Union (EU) opened Tuesday in London.
Boris Johnson said Monday that he wants a post-Brexit trade deal agreed with EU by an Oct. 15 deadline, warning that a failure of that could mean London ending its EU membership with no deal. (Photo by Han Yan/Xinhua via Getty) (Xinhua/Han Yan via Getty Images)
Extinction Rebellion protesters wearing facemasks hold up protest placards outside Shell Tower in Waterloo, London.
Extinction Rebellion are trying to step up the pressure on the fossil fuel giant to end destruction of ecosystems and communities around the world. (Photo by Dave Rushen / SOPA Images/Sipa USA)
A HS2 Rebellion tree protector climbs a mature tree in Denham Country Park in order to try to prevent its felling as part of works for the HS2 high-speed rail link on 7 September 2020 in Denham, United Kingdom. Anti-HS2 activists continue to try to prevent or delay works on the controversial £106bn project for which the construction phase was announced on 4th September from a series of protection camps based along the route of the line between London and Birmingham. (photo by Mark Kerrison/In Pictures via Getty Images)
A mural by street artist Van Jimmer on a Balfour Beatty hoarding in Lewisham, London. (Photo by Dave Rushen / SOPA Images/Sipa USA)
Supporters of WikiLeaks founder Julian Assange take part in a protest outside the Central Criminal Court, the Old Bailey in London, Monday, Sept. 7, 2020. Lawyers for WikiLeaks founder Julian Assange and the U.S. government were squaring off in a London court on Monday at a high-stakes extradition case delayed by the coronavirus pandemic. American prosecutors have indicted the 49-year-old Australian on 18 espionage and computer misuse charges over the WikiLeaks publication of secret U.S. military documents a decade ago. The charges carry a maximum sentence of 175 years in prison. (AP Photo/Matt Dunham)
LONDON, ENGLAND - SEPTEMBER 08: A woman models a Rolling Stones face mask on sale during the Rolling Stones Carnaby Street store opening at RS No. 9 Carnaby on September 08, 2020 in London, England. (Photo by Dave J Hogan/Getty Images)
Dawn over Coquet Island, a small island 1.2 kilometres off Amble on the Northumberland coast. (Photo by Owen Humphreys/PA Images via Getty Images)
Dolly the Chihuahua dog dressed as Alice in Wonderland is photographed during an Alice in Wonderland and Charlie and the Chocolate Factory themed Furbabies Dog Pageant at Jodhpurs Riding School in Tockwith, North Yorkshire, Sunday Sept. 6, 2020. (Danny Lawson/PA via AP)
A protester wears a blue outfit to represent the ocean during the demonstration.
The groups of Extinction Rebellion Marine, Ocean Rebellion, Sea Life Extinction and Animal Rebellion marched in London in a �socially distanced grief march� to demand protection for the oceans and in protest against global governmental inaction to save the seas due to climate breakdown and human interference, and the loss of lives, homes and livelihoods from rising sea levels. (Photo by Dave Rushen / SOPA Images/Sipa USA)
A police launch passes an Extinction Rebellion Marine rib boat on the River Thames during the Extinction Rebellion Macabre Beach Party.
A beach party (on grass) next to the River Thames was held by the Extinction Rebellion Marine supporters to highlight the dangers of the extreme weather caused by climate change and sound an alarm for the urgent need to take action now to avert catastrophic flooding in London, the UK and the whole world. (Photo by Dave Rushen / SOPA Images/Sipa USA)
England's Dawid Malan bats during the second Twenty20 cricket match between England and Australia, at the Ageas Bowl in Southampton, England, Sunday, Sept. 6, 2020. (Dan Mullan/Pool via AP)
A police forensics officer taking photographs in Irving Street, in Birmingham after a number of people were stabbed in the city centre, Sunday, Sept. 6, 2020. British police say that multiple people have been injured in a series of stabbings in a busy nightlife area of the central England city of Birmingham.(Jacob King/PA via AP)
Commuters arriving at Leeds railway station. Train services will be ramped up from today as schools in England and Wales reopen and workers are encouraged to return to offices. (Photo by Danny Lawson/PA Images via Getty Images)
SOUTHAMPTON, ENGLAND - SEPTEMBER 06: Jos Buttler and Eoin Morgan of England talk following their victory during the second Vitality International Twenty20 match between England and Australia at The Ageas Bowl on September 06, 2020 in Southampton, England. (Photo by Dan Mullan/Getty Images)
LEIGH, ENGLAND - SEPTEMBER 06: Kirsty Smith of Manchester United Women tackles Guro Reiten of Chelsea Women during the Barclays FA Women's Super League at Leigh Sports Village on September 06, 2020 in Leigh, England. (Photo by James Gill - Danehouse/Getty Images)
A general view inside the room where the Manchester Arena Inquiry will be held, at Manchester Magistrates Court, Manchester. The inquiry will investigate the circumstances surrounding the deaths of 22 people following the attack on May 22, 2017. (Photo by Peter Byrne/PA Images via Getty Images)
Discover More Like This
BACK TO SLIDE
The Prime Minister was joined by Mr Gove in attempts to drum up support for the UK Internal Market Bill ahead of a Commons debate on Monday.
"We're doing our part – generously – to help protect the EU's own single market, but we're clear that what we can't have even as we're doing all that is the EU disrupting and putting at threat the integrity of the United Kingdom," Mr Gove told BBC Breakfast.
"These steps are a safety net, they're a long-stop in the event, which I don't believe will come about but we do need to be ready for, that the EU follow through on what some have said they might do which is in effect to separate Northern Ireland from the rest of the United Kingdom."
Mr Gove conceded that "we are reaching a crunch moment", but insisted "we have got the support of our own MPs".
Both Ireland and the EU have warned that Mr Johnson's plans pose a serious risk to the peace process rather than protecting the Good Friday Agreement.
But he doubled down, and argued it is "crucial for peace and for the Union itself" and said voting the Bill down would reduce the chances of a trade deal with the EU, which is hanging in the balance.
Mr Johnson said the EU would use an "extreme interpretation" of the Northern Ireland Protocol to impose "a full-scale trade border down the Irish Sea" that could stop the transport of food from Britain to Northern Ireland.
"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," he wrote in the Telegraph.
He also held a conference call with around 250 MPs to try and drum up support for the Bill, and warned them against a return to the "miserable, squabbling days of last autumn".
But during the call in which there were connection issues and no questions taken by Mr Johnson, further fall-out emerged from the EU.
Leaders in the European Parliament said they would "under no circumstances ratify" any trade deal reached if "UK authorities breach or threaten to breach" the Withdrawal Agreement.
Mr Johnson appeared not to have ended the disquiet within his party during the call, with senior backbencher Sir Bob Neill saying he was not reassured by the speech.
Sir Bob, who chairs the Commons Justice Committee and is tabling an amendment to the Bill which he says would impose a "parliamentary lock" on any changes to the Withdrawal Agreement, said he still contends it contains "objectionable" elements.
"I believe it is potentially a harmful act for this country, it would damage our reputation and I think it will make it harder to strike trade deals going forward," he told Channel 4 News.
Conservative former leaders Theresa May, Sir John Major and Lord Howard are among the Tories urging Mr Johnson to think again and remove the threat to breach international law.