Government seeking to have Article 50 decision overturned as protesters gather

The British government launched a Supreme Court battle on Monday over who has the power to trigger the formal process of leaving the European Union, seeking to overturn a legal ruling that could derail its Brexit strategy.

With passions inflamed by the June vote to leave the EU, demonstrators gathered outside the court as it began hearing the government's appeal against a ruling that ministers needed parliament's assent before triggering the complex process.

EU supporters in judges' robes and wigs rode a double decker bus past the court, along with a van emblazoned with the slogan "The Brexiteers have failed us all". Rival Brexit supporters waved placards saying "This is an establishment stitch-up".

The High Court ruled last month that Prime Minister Theresa May could not trigger Article 50 of the Lisbon Treaty and begin two years of Brexit talks with the 27 remaining EU members without parliamentary backing.

If the Supreme Court upholds the earlier ruling, that could disrupt May's planned timetable for invoking Article 50 by the end of March, and give lawmakers opportunities to water down the government's policies on what the terms of Brexit should be.

Launching the government's case, its top lawyer said the earlier legal ruling was wrong, arguing that parliament had accepted before the referendum that ministers would use executive "prerogative" powers to implement its result.

"The triggering of Article 50, we say, will not be an exercise of prerogative power on a whim or out of a clear blue sky," said Attorney General Jeremy Wright.

"It is a logical conclusion of a process in which parliament has been fully and consciously involved."

The hearing is due to last for four days and for the first time in the Supreme Court's seven-year history, all 11 justices are sitting. The verdict is expected in January.

Some politicians and newspapers have portrayed the legal battle as an attempt by establishment judges to thwart the popular will.

Voters opted to leave the EU by 52 to 48 percent in June's referendum.

The Daily Mail newspaper called the High Court judges "enemies of the people" after last month's ruling.

"We are aware of the strong feelings associated with the many wider political questions surrounding the United Kingdom's departure from the European Union," Supreme Court President David Neuberger said in opening remarks. "However ... those wider political questions are not the subject of this appeal.

"This appeal is concerned with legal issues and, as judges, our duty is to consider those issues impartially, and to decide the case according to the law. This is what we shall do."