London (AFP) - The battle over Brexit reached the High Court on Thursday in a legal challenge to Prime Minister Theresa May's right to start negotiations for Britain to leave the EU without a vote in parliament.
The move could delay Brexit if successful and set up an unprecedented constitutional face-off between the courts and the government.
It was launched after Britain's June 23 referendum, which saw 52 percent of Britons vote to leave the European Union in a shock result that plunged the value of the pound and raised global economic fears.
The case seeks to challenge May's assertion that she has the right to trigger notification of Article 50 of the EU's Lisbon Treaty, which would spark two years of negotiations on Britain's departure from the bloc.
The government says it has "royal prerogative" -- a type of executive privilege -- to negotiate Brexit without needing a legally-binding parliamentary vote.
"The issue in this case is not whether this country should remain a member of the EU, or leave the EU," argued lawyer David Pannick, acting for several different individuals who brought the challenge.
"The question is whether the government may take action unilaterally to notify, or whether it needs parliamentary approval to do so."
He said deploying the royal prerogative was unlawful because under the European Communities Act 1972, it was for parliament to decide whether or not to maintain the rights contained within it.
"Notification has the consequence of depriving individuals of rights which they currently enjoy under the 1972 act," he said.
A few protesters for and against the legal action rallied outside the court in London as lawyers and claimants arrived for the first hearing.
A man holding an EU flag shouted "Parliament must vote!", while another distributed leaflets urging people to "Uphold the Brexit vote".
But those behind the legal challenge -- including an investment fund manager, a hairdresser and an expatriate living in France -- argue such a process cannot begin without a law passed by parliament.
Gina Miller, co-founder of investment fund SCM Private, wants parliament to legislate on the terms of Brexit before May can trigger Article 50.
"This is not about whether we should stay or leave -- this is actually about how we leave," Miller told AFP on Wednesday.
The fund manager is being represented by Mishcon de Reya, a prestigious law firm whose offices were picketed by pro-Brexit campaigners in July for taking on the case shortly after the referendum.
- Sturgeon eyes independence -
Although May has accused the claimants of trying to "subvert" the result of the referendum, the prime minister on Wednesday signalled she would let parliament scrutinise her Brexit plan before starting the formal EU exit process.
But she stopped short of agreeing a vote for MPs on her plan before the government triggers Article 50.
May has promised to start Brexit procedures by the end of March 2017, a timetable which could be delayed for months if Miller and her fellow claimants win their case.
Meanwhile Scottish First Minister Nicola Sturgeon unveiled plans for a new independence referendum in case her demands for more autonomy and for Scotland to stay in Europe's single market are not met.
Sturgeon said she would publish a draft referendum bill next week.
"I am determined that Scotland will have the ability to reconsider the question of independence and to do so before the UK leaves the EU if that is necessary to protect our country's interest," she said.
Some 62 percent in Scotland voted for Britain to stay in the EU.