England's Supreme Court ruling on Boris Johnson's decision to prorogue amid Brexit turmoil threatens to unravel the agreement that has kept the nation's courts and government out of each other's business for 330 years.

^{Richard Bestic explains the case outside the UK's Supreme Court}

Once known around the world as the epitome of everything politically stable, Brexit has thrown Britain's so-called "Mother of Parliaments" into chaos and confusion.

Parliament has been shut down by the government and 11 robed judges of the UK's Supreme Court have been called in to sort it out.

In other words, Britain's judges – famously apolitical – will be ruling on an issue that couldn't be more mired in the intrigues of politics.

The case is unprecedented.

At heart, the UK's Supreme Court is being called on to say whether Prime Minister Boris Johnson overstepped his powers by closing Parliament – or proroguing, as it is known.

And even whether he misled the Queen over his reasons – something the British premier has vehemently denied.

On Wednesday, the government was accused of "low, dishonest, dirty tricks" by a lawyer arguing that the move was illegal.

The government's own representative countered that matters of politics should not be subject to the law courts because they were the exclusive domain of elected Members of Parliament.

While the lawyers expressed their views in finely honed rhetoric, outside on the street noisy protesters shouted and waved home-made flags.

Johnson said he needed five weeks without Parliament to prepare his government for a Queen's Speech in the autumn, when Queen Elizabeth II would outline the government's plans for the year ahead.

The trouble is, just about everyone else in Parliament and many others insist there is only one show in town – Brexit.

And to close the building at what opposition parties call a time of "national emergency" has nothing to do with Johnson's "exciting" platform of policies.

Rather, it has everything to do with preventing Parliamentary scrutiny.

Two pillars of the establishment

The prime minister has said repeatedly Britain will be leaving the European Union on 31 October, regardless of whether the country has in place transitional trading arrangements with the European Union.

Operation Yellowhammer, a government report on the possible consequences of such an act, warned of possible shortages of food and medicine and violence in the streets.

Scotland's highest civil court, the Court of Session, has already ruled on Johnson's Parliamentary shutdown. It accused him of acting unlawfully, that he was guilty of attempting to "stymie" Parliament and that he did mislead the Queen with his legal advice.

The English High Court rejected a similar case, saying the government's action was purely political and it didn't have the power to make a judgment.

The Supreme Court will decide which court is correct and by doing so could possibly set a precedent that overturns a deal between Britain's courts and government that dates back 330 years.

It was the Bill of Rights in 1689, which effectively had the two pillars of the British Establishment agreeing that they would keep their noses out of each other's business.

Brexit might end that centuries-old understanding, as the once famously stable elements of British society slowly unravel under its disruptive pressures.

The Supreme Court could give its decision by the end of this week or the start of next week. 

If it goes against the government, Members of Parliament could return to work immediately. If not, they won't be back at their desks until 14 October – just a couple of days before a critical European Union summit. 

That summit will be Britain's last chance to come up with a deal acceptable to the EU before it crashes out of the trading bloc after 40 years of membership. 

Buckle up Britain, because as even the UK government admits, it's going to be a bumpy ride.