LONDON — Britain’s top judges vowed Monday to consider with impartiality the contentious question of who has the power to trigger the UK’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.