Mr. Johnson has been battling Parliament over his pledge to pull Britain out of the European Union on October 31 - with or without a withdrawal agreement.
"It's vital, whatever happens, that we prepare for no-deal".
Following three days of intense arguments as the Brexit battle switched to the highest court in the land, judges are set to decide on Johnson's advice to Queen Elizabeth II to suspend parliament for five weeks to October 14.
Lawyers representing the prime minister told the court during the two previous days of hearings that the dispute over the suspension was a political issue, not a matter for judges, and that Johnson's goal was not improper.
"We are both concerned about what is happening in Britain right now and the confusion that is spreading out from there to Europe".
The three-day hearing described as extraordinary at various levels witnessed leading barristers appearing on behalf of the contending parties: the Johnson government, Indian-origin campaigner Gina Miller, the Scottish government, MPs as well as Major. The inescapable conclusion from Mr. Johnson's actions, Mr.
While Remainers in the House of Commons have passed a law forcing Prime Minister Johnson to ask another extension of Article 50 should a new treaty not be agreed, it may turn out that the Europeans block any further Brexit delays and force a clean exit on Halloween.
There will also be an intervention on behalf of John Major, a former prime minister whose years in office between 1990 and 1997 were marked by bitter divisions and conflict within his own Conservative Party over Britain's relations with the EU. He opposes a no-deal Brexit and has criticized Mr. Johnson's approach as "bluster and threat". His opponents say the real reason why he sought the suspension was to prevent parliament from interfering with his Brexit strategy. In his recently released memoirs, Mr. Cameron accuses Mr. Johnson of lying during the referendum and caring only about his political future when he made a decision to co-chair the Vote Leave campaign.
Top Brexit MEP Guy Verhofstadt, who runs the group of lawmakers tasked with Brexit issues, pointed out that this debate can not take place in Britain, because parliament has been suspended there. He added that as a new prime minister he also wanted to start a fresh session with a throne speech to outline his priorities.
In a written submission, Major said Johnson had not provided a sworn statement explaining the reasons for suspending Parliament, and argued that "his failure or refusal to do so is conspicuous".
"This is forbidden territory" and takes the court "into an ill-defined minefield that the courts are not properly equipped to deal with", he said.
The document, submitted to the court by Johnson's lawyers, was disclosed as Britain's top judicial body was hearing a third and final day of legal arguments on whether the prime minister's decision to suspend parliament from September 10 to October 14 was lawful.
"If the United Kingdom wants to discuss alternatives to the existing exit agreement, then these must be presented before the end of the month", Rinne said after meeting French President Emmanuel Macron in Paris on Wednesday.
According to a European source, the Brexit timetable will also be discussed at a meeting between Johnson and Juncker on the margins of the UN General Assembly in NY next week. The post rotates among European Union members, and Finland's term runs until the end of the year.
The main sticking point over a Brexit deal is the Irish border backstop, which would require Britain to respect European Union trade and customs rules in order to avoid a hard border between European Union member Ireland and the U.K.'s Northern Ireland until a better solution is found. He has yet to provide any written proposals.