Piers Portman, 50, the son of Edward, 9th Viscount Portman of Bryanston, confronted Gideon Falter as he got out of the lift at Westminster magistrates court in June 2018.
Mr Falter, the chief executive of Campaign Against Antisemitism, was at court to see the sentencing of a woman who had posted songs on YouTube mocking the Holocaust.
On his way out of the courthouse he encountered Portman, a supporter of the defendant who wanted to shake his hand, but was rebuffed.
Southwark Crown Court heard Portman shouted “Jewish scum” at Mr Falter as he was cornered in the lift and then pursued him through the court building while “enraged” and continue to shout at him.
Jurors also heard how the Harrow-educated aristocrat had previously sent an abusive email to Mr Falter’s organisation displaying open hostility towards Jews.
Portman, whose family owns large parts of Marylebone, denied but was convicted of one count of racially aggravated intentional harassment, alarm or distress.
“Antisemitism has no place in our society and will not be tolerated”, said Sati Dhadda, from the CPS.
“Piers Portman’s conduct was disgraceful and utterly audacious in a courthouse. No-one should be subjected to such abuse based on their race or religion.
“During the trial the prosecution was able to present evidence from a previous email sent from Portman to the victim, which clearly demonstrated his hostility towards Jews. The victim also supported the prosecution and attended court to give evidence. He told jurors he had never encountered Portman before the incident and had been left shocked by it.
“I hope this conviction gives other victims of hate crime the courage to come forward in the knowledge that they will be supported through the criminal justice system.”
Portman is due to be sentenced on October 22.
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