Tens of pro-Brexit and Eurosceptic activists staged rival demonstrators outside the Supreme Court on Monday (5 December). The protests coincided with the first day of the government appealing a ruling from the High Court in November.

The decision meant MPs would have to vote on triggering Article 50, the mechanism to split from the EU. The British government, led by Attorney General Jeremy Wright, had unsuccessfully argued that Theresa May and her ministers had the legal authority – residual prerogative powers – to make such a move.

Investment fund manager and Remain voter Gina Miller was the lead claimant in the High Court case. She was pictured on Monday entering the Supreme Court for the Article 50 hearing.

Pimlico Plumbers boss Charlie Mullins, a Conservative pro-EU campaigner, was also seen entering the court.

The four-day-long hearing will be overseen by 11 justices, with a final ruling expected in January 2017.

The outcome of the historical case could have a detrimental impact on May's Brexit plans. The prime minister has promised the British electorate and EU leaders that she will trigger Article 50 by March 2017.

But Labour leader Jeremy Corbyn has vowed to put down an amendment to any Article 50 bill in the House of Commons, a move which would delay the Brexit process. The UK voted 52% to 48% to split from the EU in a 23 June referendum.

You can watch the Supreme Court hearing live here.

Pro-Europe protestors dressed as Supreme Court Justices stand outside the Supreme Court ahead of the first day of a hearing into whether Parliament's consent is required before the Brexit process can begin in London Leon Neal/ Getty Images