(Bloomberg) -- The century-old Portland stone building of the U.K.’s Supreme Court stands on London’s Parliament Square, separated from the historic structures housing lawmakers and religious leaders by about 400 feet.
The top court was founded seven years ago to ensure that politics and the judiciary never mix. That balance faces an unprecedented test as early as Dec. 5, when lawsuits seeking to delay Prime Minister Theresa May’s plan for exiting the European Union are heard.
"It will be the most important constitutional case that court will have heard," said Robert Thomas, a professor of public law at the University of Manchester. "It’s such a big constitutional issue, testing the relationship between parliament, the courts and the government in the light of the referendum."
A panel of three senior judges said Thursday that Parliament must hold a vote before starting a two-year countdown to Brexit, in a ruling that sidestepped political allegiances to focus on constitutional law.
"Nothing we say has any bearing on the question of the merits or demerits of withdrawal by the United Kingdom from the European Union: nor does it have any bearing on government policy because government policy is not law," the judges said in the ruling.
No matter how hard they tried, though, the decision was seized upon by politicians and elements of the U.K. press who campaigned to leave the EU.
"Unelected judges calling the shots: this is precisely why we voted out," David Davies, a Conservative Party lawmaker, tweeted after the ruling. U.K. Independence Party interim leader Nigel Farage said he was worried “every attempt will be made to block or delay the triggering of Article 50.”
Some of the U.K.’s national papers cried foul over the decision claiming that judges had no place meddling in a democratic process. The Daily Mail featured pictures of the three judges over a headline in all capitals that said "ENEMIES OF THE PEOPLE" on its front page while the Daily Telegraph billed the ruling as the "Judges Versus the People."
“Today’s a bad day for the constitution not because of Brexit case but attacks on independent judiciary and rule of law," the U.K. Criminal Bar Association said on Twitter.
Still, lower court triumphs don’t guarantee a final victory. Among the 92 appeals heard at the Supreme Court in the 12 months from April 1, 2015, 34 were successful and 31 were dismissed, with just two being referred to the European Court of Justice in Luxembourg.
The Supreme Court could refer the suit to the ECJ if any of the lawyers raise issues around EU law, said Dr. Nikos Skoutaris at the University of East Anglia.
"I do not think that this is likely: I think the government and the Supreme Court would try to avoid it," he said.
The Supreme Court was set up in October 2009 to remove the top judges, then known as the Law Lords, from Parliament’s unelected House of Lords after 600 years.
The court is comprised of 11 full-time justices, who are appointed by a commission overseen by court president David Neuberger, also known as Lord Neuberger of Abbotsbury. The justices that will hear the case include just one woman, deputy Brenda Hale, and a former superstar barrister, Jonathan Sumption, who once represented Russian billionaire Roman Abramovich in his fierce court fight with the late Boris Berezovsky.
Where cases in lower courts are broad expositions of evidence and disclosure, hearings in the Supreme Court are more akin to legal seminars with judges and barristers arguing the most minute parts of the law. In many ways, the Article 50 suit is the perfect test of the court’s capabilities.
The most complex cases usually see five justices sit on the panel but, because of the importance of the Brexit question, the full panel is likely to hear the appeal for the first time.
"If that happens, it’s quite exceptional," Thomas said.
In a 2011 lecture at the University of Cambridge, Sumption warned against courts trespassing into matters of government.
"For those who are concerned with the proper functioning of our democratic institutions, the judicial resolution of inherently political issues is difficult to defend," he said in the 2011 F.A. Mann Lecture.
The court has heard some of the most significant challenges to the power of the British government.
In March 2014, the judges cleared the way for the publication of secret letters written by Prince Charles to government ministers, declaring that an attempt by politicians to keep them secret was unlawful.
Two years earlier, Dominic Grieve, then attorney general, said the letters contained the Prince’s “most deeply held personal views and beliefs.” Following a challenge by the Guardian newspaper, judges led by Neuberger said Grieve didn’t have the power to veto a freedom of information tribunal, which had decided in favor of publication.
In June 2014, the court upheld a ban on doctors helping patients to end their lives. However, five of the nine judges ruled that the court has the power to declare the law on suicide incompatible with human rights legislation.
In 2013, the court dismissed two claims by prisoners who argued their rights were breached because they weren’t allowed to vote in elections.
These cases "totally pale in comparison" to the Brexit challenge, said Jeff King, a professor at University College London. Brexit "will be the most important case in terms of the consequences by a long shot."