LONDON — The impassioned speeches and howls of dissent from the backbenches, the midnight votes and archaic rituals of Parliament gave way this week to a quieter drama in Britain, as the anguished debate over Brexit shifted from the House of Commons to the country’s Supreme Court.
At the courthouse, across a leafy square from the Houses of Parliament, the scene was, by comparison, mind-numbingly dull: lawyers walking a panel of 11 justices through thousands of pages of technical legal arguments, apologizing profusely when the judges got lost in the mountain of paper.
But the stakes are every bit as high, both for Prime Minister Boris Johnson and for the role of the courts in Britain’s parliamentary democracy.
At issue is whether Mr. Johnson broke the law in suspending Parliament earlier this month. A Scottish high court ruled that he did; an English court ruled that he did not; and Britain’s highest court is hearing appeals of both cases. It is expected to rule sometime after three days of oral arguments end on Thursday.
If the court upholds the Scottish ruling, it would be a stinging rebuke of Mr. Johnson, endorsing that court’s argument that he disbanded Parliament to stymie a debate over his plans to leave the European Union, with or without a deal, by Oct. 31. He could also be found guilty of misleading the queen, who authorized the suspension, or “proroguing,” of Parliament, at his request.
For the nation’s highest court, however, the implications of such a ruling would be even more far-reaching. It would inject the court into the kind of contentious political debate it has historically avoided and push the boundaries of its purview to settle disputes in Britain’s political system.
“We’re in uncharted territory,” said James Grant, a senior lecturer in law at Kings College London. “Whether the court decides to intervene or not, its decision will break new ground and will be politically controversial. There is no escaping that.”
Mr. Grant said he believed it would be dangerous for the Supreme Court to side with the English court, which ruled that Mr. Johnson’s decision to suspend Parliament was not a matter for the courts to judge. The suspension, he argued, clearly deprived the House of Commons of its responsibility to scrutinize the government’s policy on Brexit, an issue of critical national importance.
But other legal experts worry that upholding the Scottish ruling would set a troubling precedent. It would open the door, they say, to a form of judicial review that is widely accepted in the United States, which has a codified constitution and a Supreme Court that actively interprets it.
Britain, by contrast, relies on an unwritten set of traditions and conventions that have treated a sovereign Parliament as the supreme law of the land. Once the courts venture into the political sphere and begin passing judgment on Parliament’s actions, legal analysts say, there is no going back.
“If the court accepts the invitation to devise a legal rule, there will be no logical limit to the extent that the court might want to replace conventional rules with legal rules,” said Sir Jonathan Sumption, a former justice of the Supreme Court, who is a leading commentator on the court’s role in society.
“I question the need for a judicial intervention,” Sir Jonathan said, “but I think it may happen because people are shocked by what the government has done.” Mr. Johnson’s decision to suspend Parliament, he said, was the equivalent of “taking an ax to the political convention.”
Both sides of this case have unfolded in hours of legal arguments, which are being livestreamed by the BBC and other British news organizations (cameras in the courtroom are another difference between Britain’s Supreme Court and its American counterpart). Among those submitting arguments to the justices was a former prime minister, John Major, who has fiercely criticized Mr. Johnson’s actions.
The case has commanded the headlines in Britain. But the televised images of justices staring into computer screens — often interrupting the lawyers to figure out what page they needed to scroll down to — are worlds away from the spectacle in Parliament the previous week. It has served mainly to underscore the differences between the court and other British institutions.
For one, it was founded only in 2009, after a constitutional reform process initiated by Prime Minister Tony Blair, though its roots date back far longer, through its predecessor body, the Appellate Committee of the House of Lords.
Still, the court has none of the antiquarian traditions of Parliament or even other British courts. Barristers do not wear powdered wigs. The justices are seated behind a polished, modern semicircular table, not on a raised dais. Except for ceremonial occasions like the opening of Parliament or the swearing-in of a new justice, they do not wear robes, but regular business attire.
The chief justice, known as the president, is Baroness Brenda Hale, who served as a Lord of Appeal in the House of Lords. She is one of three women now on the court. Justices are required to retire by the age of 75.
The queen appoints justices, on the recommendation of the prime minister. Until now, that process has stirred none of the furor that accompanies Supreme Court appointments in the United States. But some worry that could change if the court takes a more activist role in the ruling on cases.
After the Scottish ruling, one of the ministers in Mr. Johnson’s government, Kwasi Kwarteng, said it raised questions about whether the judges were politically motivated — a suggestion that drew widespread criticism in a country that prizes the independence of the judiciary.
Lawyers for the government warned the court that it would be “constitutionally inappropriate” to intervene in this case. But the Supreme Court has thrust itself into the Brexit debate once before.
In January 2017, in a case brought by a Guyanese-British businesswoman and activist, Gina Miller, it ruled that Mr. Johnson’s predecessor, Theresa May, needed to obtain the approval of Parliament before Britain triggered the formal procedure for withdrawing from the European Union (Ms. Miller is a plaintiff in one of the current cases).
Legal analysts said Brexit had so badly fractured the political debate in Britain that the court may conclude it has little choice but to become more involved in settling disputes, especially given Mr. Johnson’s aggressive tactics. The prime minister has even left open the possibility that he will defy Parliament’s law barring him from exiting without an agreement with Brussels.
Britain is not alone in seeing more activist courts as a response to political dysfunction. “We’re in an era, in many parts of the world, where we see a lot of political questions being tossed to the courts,” said Tom Ginsburg, a professor of law and political science at the University of Chicago.
While Mr. Ginsburg said Parliament’s suspension raised thorny questions of parliamentary sovereignty, he said he would be surprised if the court upheld the Scottish ruling. The judges, he predicted, would view such a ruling as opening the door to a regular judicial review of government policies.
“Once you have a court that is designated with this power,” he said, “there is a natural tendency toward the judicialization of politics. Once you have the court in this position, and the U.K. isn’t there yet, is there a moral hazard?”