He added that he had “been told to go and die in the gas chambers”. In one Facebook post, seen by the JC, Dr Ozarow was called a “Jew-hating Jew C**t”.
In her letter, Ms Formby, who is expected to leave her position after Sir Keir Starmer's election as Labour leader on Saturday, revealed that the abuse has led to Dr Ozarow standing down as chair of his local Labour branch, which she called "absolutely devastating".
She accused the local Conservative party of having used “similar tactics” during December's General Election against Labour's Hertsmere candidate Holly Kal-Weiss.
Writing to Mr Mabbutt, who is the party's most senior member of professional staff, she said: “I hope you will agree that this utterly disgraceful and potentially illegal behaviour has absolutely no place in politics or anywhere in society...
“Dan has spoken about how this has made him feel and, in fact, it has now driven him to stand down as the chair of his local Labour Party, which I think is absolutely devastating."
She said that “whoever is responsible for [the attacks] must be rooted out and dealt with swiftly and robustly”, adding Labour reserved the right “to take any action we consider to be necessary to resolve this matter”.
A Conservative Party spokesperson told the JC: “We do not comment on ongoing police investigations.”
A spokesperson for Hertsmere Conservatives said the letter of complaint had allowed them to give a "thorough and open account" of the election campaign.
They added: "None of our local members, during the Kenilworth by-election campaign, acted inappropriately.
"Mr Ozarow is wholly mistaken in his assertions about local Conservative party members and we are saddened such allegations continue to be repeated."
