Supreme Court to rule if May can start Brexit without parliament

British Prime Minister Theresa May will learn on Tuesday whether parliament must agree to the triggering of Britain's exit from the European Union, potentially giving members of parliament who oppose her plans a chance to amend or hinder her Brexit vision.

The UK Supreme Court will give its ruling at 9:30am (10:30 CET) in a landmark case on whether May can use executive powers known as known as "royal prerogative" to invoke Article 50 of the EU's Lisbon Treaty and begin two years of divorce talks.

The outcome of the Supreme Court case, heard by all 11 justices over four days in December, will not overturn the referendum result but determine which course towards leaving the EU is lawful.

"We are not being asked to overturn the result of the EU referendum," David Neuberger, President of the Supreme Court said at the conclusion of a four-day hearing. "The ultimate question in this case concerns the process by which that result can lawfully be brought into effect."

UK Prime Minister Theresa May has said she wants to invoke Article 50 - by the end of March.

Neuberger will read out a summary of the court's findings in a brief session expected to last five minutes.

Challengers, led by investment manager Gina Miller and backed by the Scottish government and others, say May must first get members of parliament approval as leaving the EU will strip Britons of rights they were granted by parliament.

That view was backed by London's High Court, prompting the government to appeal to the Supreme Court, the UK’s highest judicial body.

If May wins the case, she can follow her planned timetable for invoking Article 50 by the end of March.

If she loses - a more likely eventuality according to legal experts - she will probably need to bring in a parliamentary bill that will open up the Brexit process to scrutiny from members of parliament.