British Prime Minister Theresa May announced earlier this month her government will trigger those negotiations by the end of March, putting the country on course to leave the European Union by early 2019.

Financial entrepreneur Gina Miller's lawsuit against the government seeks to answer this as well as much bigger questions about where power lies in this nation's democracy and whether rights can be revoked without a vote of lawmakers.

Critics have warned that loss of access to the single market would harm British businesses by denying them a marketplace of 500 million consumers free of tariffs.

The Nov. 6-8 trip, May's first bilateral visit to a country outside Europe since she took office in July, will be in pursuit of her ambition of forging a new global role for Britain after it leaves the European Union, May's Downing Street office said in a statement.

After several hours of making submissions on her behalf on the first day of the hearing, Lord Pannick QC told the court that his client had received further "abuse, threats and insults".

The litigants, which also include a hairdresser, British expatriates and a group which calls itself the "People's Challenge", say that Britons' rights established by a 1972 act of parliament can not be withdrawn by the government alone and that the referendum was only advisory.

The case has huge constitutional importance and should provide clarity on whether executive powers can, in effect, trump an act of Parliament.

"It's a long, long running dispute", he said.

They go back to medieval times but are now placed in the hands of ministers. "This is just another installment of it".

Attorney General Jeremy Wright, the Government's leading law officer, will argue in court that the challenge lacks legal merit.

She said ministers were attempting to "bypass Parliament" by not seeking a vote, but opponents said it was a "naked attempt to steal the referendum by the back door". "We do not believe this case has legal merit".

He argued that the Government "cannot lawfully use the royal prerogative to notify under Article 50 because notification has the effect of depriving individuals of rights which they now enjoy under the 1972 Act and under other legislation". And also to stick unconditionally to the treaty rules and fundamental values.

If the court challenge is successful, the government could be forced to pass legislation authorizing Article 50 to be triggered, requiring a vote by lawmakers, the majority of whom voted to Britain to remain in the EU.

His comments came after Mr Johnson suggested that Britain can get a trade deal that is "of greater value" to the United Kingdom economy than access to the European Union single market. "You don't have a Scooby", Mr. Gethins said.

The government, he said, was wrong to suggest the legal challenge "was merely camouflage" to prevent Brexit, and added that Miller "is entitled to require that the steps that will be taken must be taken in a lawful manner".