The Lord Chief Justice has criticised Lord Chancellor Liz Truss for failing to publicly defend judges involved in the landmark Brexit ruling.
Lord Thomas of Cwmgiedd, who was one of the High Court judges who ruled Parliament, not the Prime Minister, had the final say on triggering Article 50, said Ms Truss had been "constitutionally wrong" not to stand up for judges in the face of strong press criticism.
The Lord Chief Justice criticised Ms Truss's stance that it was not her role to tell the media what to write.
He told the Lords Constitution Committee: "I regret to have to criticise her as severely as I have, but to my mind she was completely and absolutely wrong.
"And I am very disappointed.
"I can understand how the pressures were on in November, but she has taken a position that is constitutionally, absolutely wrong."
Lord Thomas said judges needed protection.
He told the committee: "There is a difference between criticism and abuse, and I don't think that that is understood.
"I don't think it is understood either how absolutely essential it is that we are protected because we have to act as our oath requires us without fear or favour.
"And it is the only time in the whole of my judicial career that I have had to ask for the police to give us a measure of advice and protection in relation to the emotions that were being stirred up.
"And I think that it is very wrong that judges should feel it.
"I have done a number of cases involving al Qaida, I dealt with the airline bombers' plot, some very, very serious cases.
"And I have never had that problem before."
Lord Thomas said it was the Lord Chancellor's "duty" to defend judges.
Referencing a Daily Mail headline branding the High Court judges in the Brexit case as "enemies of the people", the Lord Chief Justice told the committee: "The circuit judges were very concerned. They wrote to the Lord Chancellor because litigants in person were coming and saying 'you're an enemy of the people'."
Lord Thomas said he had intended to wait until a lecture he is due to give in June to make public his opinions on the matter, but felt the need to do so now because of Ms Truss's comments and a newspaper interview she gave last week.
He told the committee: "In short, I believe the Lord Chancellor is completely and utterly wrong in the view she takes.
"I regret to have to say that.
"It really is absolutely essential we have a Lord Chancellor who understands her constitutional duty."
Lord Thomas's intervention came after Ms Truss told the Financial Times that judges should boost their image because they will come under greater scrutiny post-Brexit.
She urged judges to "speak out about the important work they do to ensure that it is widely understood".
Defending her stance on the reaction to the Brexit case, Ms Truss told the Lords Constitution Committee earlier this month: "I think it is dangerous for a Government minister to say 'This is an acceptable headline and this isn't an acceptable headline' because I am a huge believer in the independence of the judiciary, I am also a very strong believer in the free press."