A court in Edinburgh will decide whether to block the PM from going ahead with proroguing the Houses until a full hearing of the case.
The decision is due to be handed down amid frantic efforts by MPs to prevent the UK from crashing out of the EU at the end of October.
The stage is set for a huge battle next week, with the Opposition and more than a dozen Conservatives joining forces to try to bind the PM’s hands.
Meanwhile, the government has signalled it will use all measures possible to ensure the country leaves the bloc on schedule, with or without a deal.
Tory former cabinet minister Oliver Letwin today insisted there was still time to pass legislation that could force the premier to delay the Brexit date, even if Parliament is prorogued for more than a month from the middle of September.
Sir Oliver said he hoped that by the end of next week Mr Johnson would know that he must seek an extension. He also confirmed he had been discussing the options with Speaker John Bercow.
Allies of Mr Bercow have suggested he is on a ‘suicide mission’, and is ready to bend procedure rules to help Remainer MPs in the fight with the government.
Boris Johnson (pictured at the G7 summit in France at the weekend) is braced for a huge battle next week, with the Opposition and more than a dozen Conservatives joining forces to try to bind his hands on Brexit
Allies of Speaker John Bercow have suggested he is on a ‘suicide mission’, and is ready to bend procedure rules to help Remainer MPs in the fight with the government
In an apparent attempt to assuage rebel Tories, Downing Street has said the UK’s team of Brexit negotiators will sit down with their EU counterparts twice a week during September ‘with the possibility of additional technical meetings, to discuss a way forward on securing a new deal’.
A series of legal challenges were launched after the Queen approved Mr Johnson’s request for Parliament to be suspended for five weeks from September 10.
The PM said on Wednesday that Parliament had to be prorogued so he could set out his Government’s new legislative agenda in a Queen’s speech and bring to an end the recording-breaking session which has lasted more than two years.
But MPs and others opposed to Mr Johnson’s Brexit strategy have said he is trying to limit their ability to stop the UK leaving the EU without a deal.
Mr Johnson’s most senior minister today dismissed the furore over the suspension of Parliament as ‘nonsense’.
Foreign Secretary and First Secretary of State Dominic Raab insisted only around four days of Commons sitting time would be lost in addition to the already-planned party conference break.
He told reporters at a meeting of EU foreign ministers in Helsinki: ‘The idea this is some kind of constitutional outrage is nonsense.
‘It’s actually lawful, it’s perfectly proper, there is precedent for it and actually, fundamentally, for the people watching this, they want to see that we are leaving the EU but also talking about all the other things they expect us to be addressing.’
A cross-party group of around 70 MPs and peers are backing the action at Scotland’s highest civil court seeking an interim interdict, which would stop the PM taking the option of suspension until a final decision has been made on the case.
Judge Lord Doherty heard arguments from a lawyer for the campaigners and a legal representative for the UK Government at a hearing at the Court of Session in Edinburgh on yesterday and he is due at the same court on Friday morning to make a decision on the case.
A court in Northern Ireland will also hear from lawyers representing anti-no-deal campaigners challenging the move and attempt to do the same at the High Court in London is also under way.
Lord Chief Justice Sir Declan Morgan, who sat for the short hearing at Belfast High Court yesterday, will hold a substantive hearing on Friday morning.
A third legal challenge brought by campaigner Gina Miller at the High Court in London ‘is being considered’, according to a judiciary spokeswoman.
Opposition leaders have issued a rare joint statement demanding Mr Johnson reverses his decision to suspend Parliament or put it to a Commons vote.
Labour, the SNP, the Liberal Democrats, Plaid Cymru, The Independent Group for Change and the Green Party said the PM’s actions were undemocratic, and had ‘the sole aim of stopping MPs from avoiding a no-deal Brexit’.
In a separate letter to his MPs, Labour leader Jeremy Corbyn encouraged them to join public protests against a no-deal Brexit.
He said: ‘There are also public protests across the country this Saturday, there will be a rally in Parliament Square on Tuesday evening, and I encourage Labour MPs to be present and to share our message.’
It followed thousands of people protesting outside Parliament on Wednesday evening, while there were smaller demonstrations in other towns and cities.
Leading rebel Tory David Gauke, a former justice secretary, said next week may be the only chance for MPs to stop a no-deal Brexit.
‘I think Parliament does have a responsibility to act and it may well be that next week is the only opportunity for us to do so.’
Tory former cabinet minister Oliver Letwin (pictured left in Westminster earlier this month) today insisted there was still time to pass legislation that could force the premier to delay the Brexit date. Conservative MP Richard Harrington (right) has signalled he is ready to join the revolt
The Times reported that Tory rebels have drawn up plans with Labour for Parliament to sit over the weekend of September 7-8 in order to try to pass laws to stop a no-deal Brexit.
They are expected to try to use an emergency debate procedure to try to take control of the Commons order paper – allowing them to push through legislation.
A source close to Mr Bercow told the newspaper: ‘He could go on a suicide mission. But he is on a collision course, not only with the government but the Queen and the clerks of the House.’
Mr Johnson faced resignations yesterday by Scottish Conservative leader Ruth Davidson and veteran Tory minister Lord Young, in part due to the Government’s approach to leaving the EU.
Former minister Richard Harrington – who has been a vocal opponent of Mr Johnson’s Brexit strategy – also said he will not stand again at the next general election.
The UK’s chief Brexit ‘sherpa’ David Frost met this week with the EU’s Article 50 Taskforce and agreed that talks would be intensified.
However, the EU’s chief Brexit negotiator made it clear he was not ready to retreat on the issue of the Northern Ireland backstop, despite pressure from the Prime Minister.
Mr Barnier tweeted: ‘PM @BorisJohnson has said that the UK will leave the EU on 31 Oct. In all circumstances, the EU will continue to protect the interests of its citizens and companies, as well as the conditions for peace and stability on the island of Ireland. It is our duty & our responsibility.’
Meanwhile Foreign Secretary Mr Raab has announced the Foreign Office will provide up to £3 million in grant funding for charities to help UK nationals living in the EU who may struggle to complete the necessary residency applications.
He said: ‘The UK will be leaving the EU on October 31 and we want to help UK nationals living across the EU to be fully ready for Brexit, whatever the circumstances.
‘This funding will ensure people get the support they need to apply to protect their residency rights and access to services.’