In the hall of London’s Inner Temple, a grand dining chamber with stained-glass windows and coats of arms adorning the walls, 300 lawyers assembled to complain about Britain’s exit from the European Union.

“The world has effectively been turned upside down,” said former attorney general Dominic Grieve.The campaign in favour of leaving was “the constitutional equivalent of crimes against humanity,” remarked Richard Gordon, a barrister at Brick Court Chambers.

When the speakers asked if anyone in the room had anything more positive to say, there was silence. Like that audience at the Inner Temple last month, London's legal establishment was overwhelmingly in favour of remaining within the EU. No one was surprised when a handful of legal claims emerged after the referendum to challenge the Brexit process. The question is, can they delay or even derail Britain's departure from the bloc?

Article 50

The lawsuits, filed on behalf of a hairdresser, a finance entrepreneur and others unwilling to be publicly identified, have been merged into a single claim that is likely to end up before the UK Supreme Court this year. The claimants want the nation’s highest court to rule that it would be illegal to invoke Article 50, triggering the two-year countdown to Brexit, without first holding a vote in parliament.

While backers of Brexit have derided the effort as futile manoeuvring,the implications may reach far beyond the oak-panelled rooms of London’s law chambers. The case could pit the power of the judiciary against the authority of the prime minister in a manner never seen before in Britain, according to more than a dozen lawyers and judges interviewed for this article.

“This will be one of the most important constitutional law cases ever decided,” said Jeff King, a professor at University College London. Britain, unlike the US, does not have a written constitution, but rather an accumulation of laws, customs and judicial decisions that date back centuries. Among potential outcomes: a lengthy delay as legal challenges play out; the risk – albeit slight – of jail for government ministers should they ignore the court’s orders; and even a parliament that’s forced to vote and ultimately rejects Brexit. It is also possible the court will decide the government can invoke Article 50 whenever it chooses, with or without a vote.

“The court takes this litigation very seriously and will move expeditiously,’’ Judge Brian Leveson said at a preliminary hearing on July 19th. The matter is “of such constitutional importance it is difficult to see why’’ it won’t move quickly to the supreme court, he said.

Gina Miller, who runs an investment start-up, and hairdresser Deir Dos Santos, were the only two claimants identified at the hearing. Santos’s lawyer, Dominic Chambers, has described him as an “ordinary guy”. Others who considered joining the suit were put off by racist and anti-Semitic abuse, Leveson was told. Miller was undeterred.

“I don’t shy away from what I think is right,’’the 51-year-old said in an interview. Her father was the attorney general of Guyana, a former British colony in South America, and she trained as a lawyer before starting SCM Private, an online investment manager. On June 29th, Miller gave a speech at London law firm Mishcon de Reya LLP about gender equality. When one of the partners, Kasra Nouroozi, approached her to talk, she guessed what it was about.

“I instinctively looked at them and said: ‘Article 50,’” she recalled. “I just said, ‘I will do it.’’’ Miller, who supported the remain campaign, wants an “honest, grown-up’’ debate in parliament about the impact of Brexit on science, education and security, but does not want to revisit the referendum result.

“The government can stop all this any time if they turn around and say: we will follow procedural steps,’’ she said. Lisa Tremble, a spokeswoman for Mishcon de Reya, declined to comment.

‘Nonsense’

The law firm came under criticism for bringing the suit. Spiked, an online magazine focusing on politics and culture, organised a protest in front of Mishcon’s offices on July 7th.

“It’s shameful that a law firm thinks it can overrule the democratic spirit,’’ Spiked’s deputy editor, Tom Slater, told protesters waving “Invoke Article 50 NOW!’ banners.”

“The Mishcon and the Deir Dos Santos actions are at most tactical, and at worst nonsense,’’ said Philip Young, a lawyer at London firm Cooke, Young and Keidan. Parliament would respect the referendum result even if the matter came to a vote, he said. Other legal experts say triggering Article 50 without an act of parliament would be reckless. Negotiators would have just two years to hammer out new agreements with the EU before the rights of Britons abroad, or banks doing business on the continent, would disappear.

‘Dangerous path’

Oliver Letwin, the minister overseeing the preparation for exit negotiations before prime minister Theresa May appointed David Davis to head a new Brexit department, told the foreign affairs committee in parliament on July 5th that government lawyers had advised him that “it is clearly” the prerogative of the prime minister rather than parliament to trigger the exit mechanism.

In theory, May could ignore the judicial review. Konrad Schiemann, a retired UK judge who also served at the European Court of Justice, described that as a “a very dangerous path for politicians to go down”. A judge can commit a minister to prison if he or she defies a direct order from the court, though that rarely happens. In this case, the supreme court will probably provide guidance on what is legal rather than issue a binding order, Schiemann said. And the government may seek a compromise.

‘Nightmare scenario’

Still, if the government did ignore a court ruling, the case – in a head-spinning twist –could be appealed to the European Court of Justice, an authority Britons rejected when they voted to exit the EU on June 23rd.

“It’s an absolute nightmare scenario,” Schiemann said. “I suspect the government will try to avoid all these things.’’

In the past, Britain’s judges have been reluctant to infringe on parliament. In 1972, after about 300 hours of parliamentary debate, the UK signed the Treaty of Rome to join the European economic community. A year before, three judges heard a legal challenge by Raymond Blackburn, a Labour MP, who said Britain would breach its own laws by doing so. Blackburn lost. “Such decisions have nothing to do with these courts,’’ Lord Justice Cyril Salmon said at the time.

Bloomberg