UK Prime Minister Theresa May's government launches a challenge on Monday against a court ruling that it requires parliamentary approval to start the process of leaving the European Union.

If the Supreme Court dismisses the government appeal it could derail May's timetable for triggering Article 50 of the Lisbon Treaty and leaving the EU.

The case will be the most high-profile and complex one for the court where for the first time all its 11 justices will sit on the panel. The verdict is deu later in January.