LONDON (AP) — A man has been arrested on suspicion of sending online threats to the lead claimant in Britain's Brexit court case, police said Wednesday, as the high-stakes legal drama continued at the Supreme Court.

Financial entrepreneur Gina Miller took the government to court, arguing it does not have the power to trigger Britain's exit from the 28-nation European Union without a vote in Parliament.

Last month, three High Court judges agreed. The Supreme Court is hearing an appeal by the government.

Miller, 51, says she has received abuse and death threats since the Nov. 3 ruling, which raised the temperature of Britain's debate about the EU. She is attending this week's Supreme Court case with bodyguards.

London's Metropolitan Police said officers arrested a 55-year-old man Monday in Swindon, western England, "on suspicion of racially aggravated malicious communications" directed at a 51-year-old woman since Nov. 3.

The suspect has been bailed while prosecutors consider whether to charge him. A 38-year-old man from Scotland has also been issued a "cease and desist" notice as part of the same investigation.

Miller's lawyer, David Pannick, was grilled by judges Wednesday as he argued that the government does not have the power to take Britain out of the EU — removing rights granted to citizens by membership in the bloc — without the approval of lawmakers.

Prime Minister Theresa May plans to launch EU exit talks by the end of March using ancient powers known as royal prerogative, which enable governments to join or leave international treaties.

Government lawyers argue that Parliament has already had its say, by passing the 2015 law that made June's referendum on EU membership possible.

The court's most senior justice, David Neuberger, suggested to Pannick that it could be argued "Parliament has ceded this issue ... to the people" by holding a referendum.

The hearing is due to end Thursday, with the judges giving their ruling next month.