IT has been dubbed the most important constitutional court case in modern British history.

On Monday morning at the UK Supreme Court, just across Parliament Square from the House of Commons, bewigged QCs representing the UK and Scottish Governments as well as other parties will do legal battle, which will last over four days.

The political stakes are high because if the 11 Supreme Court judges rule against Theresa May and uphold the previous ruling by the High Court - that MPs should have a vote on her Brexit strategy - but also go further and accept Nicola Sturgeon’s case - that MSPs should have a vote too - then a general election in spring 2017 could be on the cards.

This is because the likelihood is that Holyrood, overwhelmingly in favour of a soft Brexit, could if it regards the UK Government prospectus as a hard Brexit, veto it.

In such a scenario and given the vital importance to the country’s economic future of how Brexit pans out, the Prime Minister may believe she has no option - if she is to get her way on how to approach Brussels on the issue - but to seek a mandate from the people by putting it in a manifesto and calling an election.

The proceedings will begin at 11am on Monday with Jeremy Wright QC, the Attorney General, setting out the UK Government’s appeal aided by James Eadie QC.

The Whitehall team will also include Lord Keen QC, the Advocate General for Scotland, Whitehall’s leading Scottish lawyer, who will seek to rebut the Scottish Government’s case that MSPs like MPs should have a vote on the UK Government’s Brexit strategy.

The appellant’s submission will continue on Tuesday and on the same day, John Larkin QC, the Attorney General for Northern Ireland, will put forward a challenge to the Brexit process that failed at Belfast High Court last month ie that the UK Government cannot use royal prerogative powers to withdraw the UK from the EU without an Act of Parliament.

On Wednesday, the court will hear the Scottish Government’s case put by James Wolffe, the Lord Advocate, who will argue because the devolved powers to Holyrood are so intertwined with EU law that MSPs should have a vote on the Brexit strategy.

The final day on Thursday will involve not just the Scottish Government’s case but the Welsh one’s too as well as other interested parties. The final session will also hear Mr Eadie responding for the UK Government.

Underlining the importance of the case will be the fact that the lay-out of the bench at which the judges sit has had to be altered. The courtroom furniture has hitherto only had to cater for nine justices but, in an historic first, will come Monday accommodate all 11.

The judges will rely heavily on their computer screens and the digital versions of case papers in order to save space in the courtroom.

Given the level of interest in the case, extra seating has been squeezed into the main court and two other courtrooms have been commandeered as overflow spaces so members of the public can watch proceedings on screens via a live video link. This will push the capacity to over 100 seats.

For those unable to get into the court, the proceedings will be live-streamed so anyone with an Internet access can watch the legal drama unfold.

The online service has been “upgraded” so the site does not crash. Some 300,000 people will be able to watch proceedings at any one time.

Given the importance of the case, more than 80 journalists from home and abroad have accredited; the highest number since the supreme court heard Wikileaks founder Julian Assange’s 2012 appeal against the validity of a European Arrest Warrant raised in Sweden. A media suite has also been established in the court building.

The key ruling by the 11 judges is due early January.