The battle for Brexit is heading for a nailbiting showdown in the Supreme Court in late October – when the deadline for crashing out of the EU will be just days away – after Boris Johnson’s new strategy was revealed.

Ministers plan to manufacture a legal fight to avoid directly breaking the law when compelled to ask for a further Article 50 extension, while also sidestepping the requirement to comply with it.

The “plan B” paves the way for an unprecedented constitutional crisis after parliament’s deadline for seeking a Brexit delay passes on 19 October – with the threat of the prime minister being jailed for contempt of court.

With the deadline for crashing out on 31 October, it will be a race against time to force Mr Johnson to Brussels before Halloween, or to bring him down in a vote of no confidence and send a replacement.

Labour condemned the strategy as behaving like “every tinpot dictator on the planet throughout history” – demanding that Mr Johnson obey the “duty” imposed by parliament.

No10 is also reported to be considering sending a letter to the EU requesting a Brexit extension, in order to meet the conditions passed by MPs last week, but then immediately sending another saying the government does not actually want a delay. Legal experts, including former attorney general Lord Falconer, warned that this would still breach the law.

If Mr Johnson disregards some or all of the bill's requirements – which is set to receive royal assent on Monday – this could lead to an emergency judicial review in the courts by MPs.

The unprecedented case would start in the High Court and the expectation is that it would very quickly move to the Supreme Court, almost certainly before 31 October.

And it triggered an extraordinary warning from the justice secretary, Robert Buckland, to obey “the rule of law”, as he denied he was poised to follow Amber Rudd by resigning.

Protesters take to streets after Boris Johnson suspends parliament Show all 11 1 /11 Protesters take to streets after Boris Johnson suspends parliament Protesters take to streets after Boris Johnson suspends parliament Anti Brexit protesters march on Whitehall EPA Protesters take to streets after Boris Johnson suspends parliament Many of the protesters carried placards AP Protesters take to streets after Boris Johnson suspends parliament A demonstrator wears a Boris Johnson mask during a London rally AFP/Getty Images Protesters take to streets after Boris Johnson suspends parliament An anti-Brexit demonstrator wields an EU flag during a London rally. AFP/Getty Images Protesters take to streets after Boris Johnson suspends parliament The protesters also marched to Trafalgar Square, where they blocked traffic AP Protesters take to streets after Boris Johnson suspends parliament John McDonnell addressed crowds in Whitehall. PA Protesters take to streets after Boris Johnson suspends parliament A small group of Brexit supporters attempted to stage a counter protest in central London. AP Protesters take to streets after Boris Johnson suspends parliament Three people were arrested in London, including a woman who sat on the road near Trafalgar Square. AP Protesters take to streets after Boris Johnson suspends parliament In Oxford, locals and students gathered outside Balliol College, Boris Johnson's alma mater, to protest. PA Protesters take to streets after Boris Johnson suspends parliament Thousands of people gather in central Glasgow to protest against the prime minister. AFP/Getty Images Protesters take to streets after Boris Johnson suspends parliament Jeremy Corbyn spoke to protesters in central Glasgow. Getty

The clashes came ahead of the likely suspension of parliament, at Monday’s close – for five weeks – when the prime minister again fails to secure he general election he craves.

It is a fight to the death for Mr Johnson, who believes he and the Conservative Party will be devoured by the Brexit Party if Brexit is lost – hence his vow to lie “dead in a ditch” rather than fold to parliament’s will.

On another dramatic day in the Brexit crisis:

* France warned it will veto an Article 50 extension, unless the UK ends the political chaos and tells the EU what it wants

* Brussels’ former top law officer rubbished No 10’s plan to sabotage the EU and make it ‘no longer legal’, arguing it made no sense.

* Ms Rudd – who was replaced as work and pensions secretary by Therese Coffey – revealed the cabinet was denied legal advice about the decision to prorogue parliament until 14 October.

* Sajid Javid, the chancellor, refused to rule out an electoral pact with the Brexit Party to secure EU withdrawal – after Nigel Farage proposed one.

* The Conservatives took revenge on John Bercow, the Commons speaker, by announcing plans to contest his Commons seat, against longstanding convention.

* Leo Varadkar, the Irish premier, vowed his country would not concede on the need for the Irish backstop, ahead of a first meeting with Mr Johnson in Dublin on Monday.

Dominic Raab, the foreign secretary, revealed the new strategy when he vowed to “test to the limit” the cross-party law to block a no-deal Brexit, which is due to receive royal assent on Monday.

It appears crystal clear in stating an extension must be sought – for at least three months – if no deal has been passed by parliament by 19 October, or if MPs have not backed a no-deal departure.

But Mr Raab told Sky’s Sophy Ridge on Sunday programme: “We will look very carefully, legally at what it requires and what it doesn’t require.”

And, pointing to the failed legal actions to stop parliament being suspended, he added: “We had two legal challenges last week and we won both of those.”

Shami Chakrabarti, Labour’s shadow attorney general, hit back, saying: “I think the position is irresponsible and elitist, the idea there’s one law for Boris Johnson and his mates and another law for everyone else – it’s appalling.”

“Every tinpot dictator on the planet throughout history has used the excuse of having the people on their side to break the law to shut down parliament and all the rest of it.”

MPs fighting a no-deal Brexit are already lining up a legal team to prepare to go to court to compel Mr Johnson to go to Brussels if necessary.

They would probably apply for an injunction after which – if he refused to comply – a judge could order an official sign off the extension “in place of the prime minister”.

At the weekend, Lord Macdonald, a former director of public prosecutions, said any citizen, including Mr Johnson, would be jailed if they failed to “purge their contempt”.