The Government’s appeal over its right to trigger Article 50 has begun at the Supreme Court.
The highest court in the land is being asked to overturn a High Court ruling that the Prime Minister must seek MPs’ approval to trigger the process of taking Britain out of the European Union.
In a decision that infuriated Brexiteers, three senior judges said Theresa May lacked power to use the royal prerogative to trigger Article 50 of the Lisbon Treaty and start the two-year process of negotiating Brexit without the prior authority of Parliament.
Now 11 Supreme Court justices - a record number to sit on an appeal - will have their say regarding one of the most important constitutional cases in generations.
The hearing will last four days but a decision is not expected until early in the new year.
If the Supreme Court appeal is unsuccessful, and any potential further appeal to the European Court of Justice in Luxembourg also fails, the Government’s plans for Brexit could be thrown into disarray.
But May has made it clear she still intends to give an Article 50 notification by the end of next March to start the leave negotiations with 27 other EU countries.
The High Court ruling was won by Gina Miller, 51, an investment fund manager and philanthropist who was selected to bring the lead case.