A law drafted by Opposition figures demanding the Brexit deadline is extended to January 2020 to avoid Britain leaving the European Union without a deal is expected to receive Royal Assent this week.
But the Prime Minister is threatening to disobey the terms and push ahead with his plan to keep no-deal on the table when he meets fellow leaders at the European Council summit on October 17.
Mr Johnson has said he would rather be “dead in a ditch” than ask the EU for an extension beyond Halloween.
The Conservative Party leader buttoned down on his position further on the weekend, telling The Mail On Sunday: “I refuse to accept (Jeremy) Corbyn’s pointless delay.”
His stance has led to speculation that more front bench ministers could walk out on the Government.
Amber Rudd sensationally quit the Cabinet and the Tory Party on Saturday, citing concerns over Mr Johnson’s approach to the Brexit negotiations.
She told the BBC’s Andrew Marr Show that “not enough work is going into actually getting a deal”.
The former work and pension secretary’s resignation set off alarm bells that more ministers could follow.
Justice Secretary Robert Buckland declared on Twitter that “speculation about my future is wide of the mark”.
Yet the QC’s comments to Mr Johnson in private about the rule of law have been read as a shot across the bows and a warning that he will not tolerate the PM breaching Parliament statute.
The Sunday Times reported that the principle plan for Mr Johnson and his chief strategist Dominic Cummings is to force an explosive showdown at the Supreme Court that could even see him risk a jail sentence to deliver on his pledge to leave the EU by October 31.
Mr Buckland said: “I fully support the Prime Minister and will continue to serve in his Cabinet.
“We have spoken over the past 24 hours regarding the importance of the Rule of Law, which I as Lord Chancellor have taken an oath to uphold.”
His predecessor David Gauke MP, who had the Tory whip withdrawn by the PM for voting with the Opposition last week, said the current “uncertainty” surrounding whether Mr Johnson will defy the will of Parliament was “damaging to the rule of law”.
The former Cabinet minister tweeted: “In the end, I don’t expect any prime minister to defy the law.
“But the uncertainty about the Government’s intentions is, in itself, damaging to the Rule of Law.
“Ministers should be clear and unambiguous - the Government will abide by the law.”
Tory grandees also weighed in, calling it “inconceivable” that a party leader would consider breaking the law.
Baron Lexden, a Tory historian, told BBC Radio 4’s The World This Weekend: “It is quite extraordinary to see Conservative politicians indicating even if they don’t say so explicitly, but allowing it to be thought on their behalf by those doing the briefing, that they might disobey the law, inconceivable in any previous generation of the Conservative Party.”
Former whip Lord George Young of Cookham, who quit his post last month, appealed for “calm” on the same programme.
“I think we need to calm down a bit, there’s been too much talk about dying in ditches, going to prison, picking up chainsaws, challenging the Supreme Court, sabotaging Brussels,” said the ex-MP.
The peer’s message of calm was not heeded by Plaid Cymru, with the Welsh party rallying Opposition colleagues to impeach the PM if he does defy Parliament.
Westminster leader Liz Saville Roberts said: “Boris Johnson has already driven a bulldozer through the constitution, so no longer are ideas like impeachment far fetched.
“I will tell other Opposition party leaders we need to be ready to impeach Boris Johnson if he breaks the law.”
Ms Saville Roberts MP remarked that Mr Johnson in 2004 wrote in favour of impeaching then prime minister Tony Blair.
Foreign Secretary Dominic Raab Sky News’s Sophy Ridge on Sunday: “We’re always going to behave lawfully as a Government, of course you’d expect that, and anyway it will be challenged in the courts, but what we are going to do with that legislation is test very carefully what it does and doesn’t require, and that’s not only the lawful thing to do, I think it’s the responsible thing to do.”
And Chancellor Sajid Javid told the BBC’s Andrew Marr Show: “Of course this Government will obey the law. We are going to continue to work towards exit on October 31. We will leave on October 31.”
Meanwhile, the Supreme Court is due to hear Gina Miller and ex-PM John Major’s appeal against the decision to prorogue Parliament for almost five weeks.
Both the Commons and the Lords are set to shut until October 14 if MPs opt not to vote for a snap general election on Monday.
The country’s judges will hear the case on September 17, after prorogation has started, along with an appeal from a similar case in the Scottish Court of Session.