Last week, Mr Johnson prorogued or temporarily shut down the Parliament until the middle of next month, just before the Brexit deadline of 31 October, with critics accusing him of trying to avoid scrutiny and deliver on his promise of getting Britain out of the EU "deal or no deal".
The prime minister has maintained that he had the right to suspend Parliament ahead of the Queen's speech on 14 October, in which the monarch is to outline the government's legislative programme for the upcoming year.
It is now up to 11 judges at the highest judicial body in the United Kingdom to consider two appeals after a Scottish court found the suspension to be "unlawful", while an English court called the matter political and not a legal one.
The prosecution has argued that the prime minister sought to "silence" the Parliament, but the British government’s defence insists that Johnson had the right to prorogue it.
"The big question here is whether or not the court will decide it has the power to make a determination on the prorogation", says Dr Roslyn Fuller, director of the Solonian Democracy Institute based in Dublin and author of 'Beasts and Gods: How Democracy Changed Its Meaning and Lost Its Purpose'. "They could, as the London court did, decide that this is a purely 'political' matter and that, therefore, as long as the process was observed they cannot examine Johnson's motives for prorogation", she said.
But if the court rules that Johnson exceeded his powers and is infringing on Parliament's by suspending it for such a long period, Dr Fuller believes it would open up the following issues for the future: "Is there a time-limit on prorogations? How important would pending business have to be to make a prorogation unlawful? How does one determine whether a politician's purpose is to 'stymie' Parliament (obviously very unusual since generally, they control Parliament)? Is it relevant that Parliament had recourse to alternatives (bringing down the government and calling an election)?"
While the Parliament has accused Boris Johnson of intending to withdraw the country from the EU without a deal, hiding related information and documents and misinforming the Queen to obtain her authorisation to suspend Parliament, political analyst and journalist Klaus Jurgens noted that despite Boris Johnson and his advisor Dominic Cummings being Brexiteers, the government’s preparations for a no-deal Brexit, dubbed "Operation Yellowhammer", were not devised under Johnson. "If there are justified suggestions [that the] government hides vital details, Theresa May would be to blame", he argued.
Jurgens also added that in his view, the outcome of the Supreme Court hearing will be in Johnson's favour: "Every late summer Parliament is prorogued due to annual party conferences. My view – prorogation lawful, perhaps length debatable".
In his turn, Geraint Johnes, professor of economics at the Lancaster University Management School, said that Johnson has put himself in a difficult situation and that it is hard to see how the PM could legally withdraw Britain from the EU without a deal at this point.
"He has painted himself into a corner and needs to negotiate a deal quickly in order to keep his promise of leaving the EU at the end of October. The difficulty will be finding a deal that is acceptable both to the EU and to the UK parliament, especially in the time available", Johnes explained.
He added that the parliamentary suspension has only prolonged the disagreement:
"The prorogation has generated a lot of controversy and its implications may be important for the way democracy works in the UK - but as far as the Brexit negotiations are concerned, Parliament has already acted to preclude a no-deal outcome", the professor said.
When it comes to possible consequences for Johnson and his plan to leave the EU on 31 October, in both scenarios Mr Jurgens believes that he will stay on as prime minister as the opposition "too weak":
"Labour is too weak to win an outright majority and Johnson will remain PM at least until after an early vote. Actually, should he remain steadfast and no matter [if there is a] structured exit, or no deal, the Tory Party is poised to come out on top as long as the Brexit Party asks their members to vote Tory just this once to secure a Tory majority, thus Brexit", the political analyst noted.
On the first day of the hearing, on Tuesday, the government's lawyer said that Johnson will obey any ruling of the Supreme Court. But can the prime minister survive if the court rules against him? This remains to be seen.
