The Supreme Court began considering the appeal on Monday. If successful, the British government will not have to consult Parliament before pulling the UK out of the EU.
The UK's Supreme Court on Monday began considering an appeal against a High Court judgement on November 3 preventing the government from beginning negotiations over Britain's exit from the EU without the approval of Parliament.
Some supporters of Brexit argue that the earlier High Court decision tramples on the will of the people by ignoring the result of a referendum in June. Defenders of the decision say it protects the constitutional principle that parliament is the United Kingdom's supreme legal authority.
Simon McGregor-Wood reports: