A man has been arrested over alleged threats against Gina Miller, the woman behind the Brexit legal challenge.
Met Police officers arrested the man, 55, in Swindon on Monday on suspicion of racially-aggravated malicious communications, police said.
He was taken to a Wiltshire police station and later released on bail.
Officers from the Met's anti-cyber crime Falcon Unit also issued a "cease and desist" notice on 3 December to a 38-year-old man from Fife, Scotland.
The Metropolitan Police said the Swindon man was held over threats made online from 3 November onwards.
'Prerogative powers' argument
Gina Miller, a partner in an investment management firm, is the lead claimant in the legal fight to get Parliament to vote on whether the UK can start the process of leaving the EU.
She and her fellow claimants - including hairdresser Deir Dos Santos and the crowd-funded People's Challenge group - won their case at the High Court in November.
The government's appeal against this ruling is currently being heard at the Supreme Court in London.
Government lawyers argue that they do not need the approval of MPs to start Brexit and can instead begin the process using "prerogative powers", a remnant of the era of all-powerful kings and queens.
Ms Miller and her co-claimants disagree, saying Parliament should first scrutinise the details of Brexit - "how we leave, how they're going to negotiate, the directions of travel the government will take".
Speaking outside court after her High Court victory on 3 November, she said: "You can't talk about getting back a sovereign Parliament and being in control but at the same time then bypass it," she said.
"It is about any government, any prime minister, in the future being able to take away people's rights without consulting Parliament. That isn't a democracy, that is verging on dictatorship."
The debate around whether Parliamentary approval is needed to trigger Article 50 of the Lisbon Treaty has been highly-charged, like the EU referendum campaign itself.
At the start of Supreme Court proceedings, its president, Lord Neuberger, warned "legal powers" existed to deal with anyone making threats and abuse towards members of the public involved in the case.
Ms Miller has told the BBC her role in the case had made her "apparently the most-hated woman in Britain".