LONDON (AP) — Britain's top judges vowed Monday to consider with impartiality the contentious question of who has the power to trigger the U.K.'s exit from the European Union — the government or Parliament.
The Supreme Court justices acknowledged that the case has aroused strong feelings over how and whether to leave the EU. It also has major constitutional implications for the balance of power between the legislature and the executive.
The court's most senior justice, David Neuberger, opened a four-day hearing by condemning the "threats of serious violence and unpleasant abuse" directed at lead claimant Gina Miller and others arguing that Parliament should have a say.
"Threatening and abusing people because they are exercising their fundamental right to go to court undermines the rule of law," Neuberger said, banning publication of the addresses of Miller and other parties in the case.
Neuberger and 10 other justices at the country's top court must decide whether Prime Minister Theresa May's government can invoke Article 50 of the EU's key treaty, the trigger for two years of divorce talks, without approval from lawmakers.
May plans to trigger Article 50 by the end of March, using centuries-old government powers known as royal prerogative. The powers — once held by the monarch but now used by politicians — enable decisions about joining or leaving international treaties to be made without a parliamentary vote.
Financial entrepreneur Miller and another claimant, hairdresser Deir Dos Santos, went to court to argue that leaving the EU would remove some of their rights, including free movement within the bloc, and that shouldn't be done without Parliament's approval.
Last month, three High Court judges agreed. But the government says they have misinterpreted the law.
Opening the government's arguments, Attorney General Jeremy Wright said the use of prerogative powers didn't undermine Parliament, because the legislature had been in the driver's seat throughout the referendum process.
Wright said the government wasn't using prerogative powers "on a whim or out of a clear blue sky" but as the result of a process in which Parliament had been "fully and consciously involved."
"When it comes to leaving the European Union, Parliament has had full capacity and multiple opportunities to restrict the executive's ordinary ability to begin the Article 50 process and it has not chosen to do so," Wright said.
Though the courtroom drama is unfolding in cool legal language, it has set public passions simmering.
November's ruling infuriated pro-Brexit campaigners, who saw the lawsuit as an attempt to block or delay Britain's EU exit. The anti-EU Daily Mail newspaper labeled the justices "enemies of the people" and suggested some held Europhile views that compromised their impartiality.
Neuberger told a courtroom packed with scores of lawyers, journalists and members of the public that all sides in the case had been asked whether they wanted any of the justices to step down. He said that "without exception," none had any objections.
A handful of pro- and anti-EU demonstrators rallied outside the court building on London's Parliament Square as the case began. Miller — who has received a torrent of online abuse for her role in the case — arrived with her lawyers to cheers from pro-EU campaigners dressed as judges atop an open-topped double-decker bus.
Former U.K. Independence Party leader Nigel Farage had vowed to lead a march on the Supreme Court to demand judges respect the will of the majority. It was canceled last week after organizers said there was a risk it could be hijacked by far-right extremists.
In a reflection of the constitutional importance of the case, all 11 Supreme Court judges are hearing the appeal, the first time the full court has sat since it was founded in 2009. They are likely to give their ruling in January.
The case is complicated by the involvement of myriad participants, including politicians in Northern Ireland, who also want a say, and the Scottish government, which argues the Edinburgh-based Scottish Parliament should get a vote too. Britons voted by 52 percent to 48 percent to leave the EU, but voters in Scotland strongly backed staying in, and the Scottish government says they shouldn't be dragged out of the 28-nation bloc against their will.
Even if the government loses, it is unlikely to stop Britain leaving the EU. A debate in Parliament could delay the timetable, but most lawmakers have said they won't try to overturn the referendum result.
They could, however, seek to soften the divorce terms and have a greater say in the government's negotiating strategy — something May and other ministers have been unwilling to disclose for fear of tipping their hand.
Opposition Labour Party lawmakers have filed a motion for debate in the House of Commons on Wednesday calling for the government to publish its plan for leaving the EU before it triggers Article 50.
May's spokeswoman, Helen Bower, accused the government's political opponents of trying "to frustrate the will of the British people by slowing down the process of leaving and trying to tie the government's hands in negotiation."
At the Supreme Court, Neuberger said the judges were "aware of the strong feelings" Brexit aroused, but insisted "this appeal is concerned with legal issues," not politics.
"As judges, our duty is to consider those issues impartially, and to decide the case according to the law," he said.
"That is what we shall do."
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