Lawyers acting for the firm challenging the prime minister’s authority to leave the European Union have been subjected to anti-Semitic abuse, a top barrister has said.

Lord Pannick QC, acting for City law firm Mishcon de Reya, told Sir Brian Leveson at the Royal Courts of Justice that racist abuse had already been directed at staff.

The firm is coordinating several efforts to challenge the government’s authority to trigger Article 50, arguing instead that only parliament can collectively start the process of leaving the EU, following this year’s Brexit vote.

However, the firm founded by Victor Mishcon, is now being targeted for anti-Semitic abuse, said Pannick, who is also Jewish.

“The publicity that has accompanied notification of the legal issue has provoked a large quantity of abuse directed at my solicitors,” said Pannick. “It is racist abuse, it is anti-Semitic abuse and it is objectionable. It is contempt of court for people to make threats.”

He asked Leveson, who is also Jewish, whether the names of claimants should be redacted, given the abuse, saying: “People have been deterred from [making legal claims]… “It is a very serious criminal matter for people to make threats.”