Jon Lansman, the founder of left-wing group Momentum, has been subjected to antisemitic abuse after announcing his decision to stand for the role of Labour Party general secretary.
Mr Lansman had defied calls from senior Labour figures not to stand and allow the Unite union backed-candidate Jennie Formby a clear run for the role as the party’s top official.
But the Momentum chief is said to have refused to back down, insisting it would be bad for democracy within Labour if he did so.
In response, he was subjected to repeated abuse on social media – with much of it focusing on his Jewish background.
One post on Twitter written from an account in the name of @TheBirmingham6 labelled Mr Lansman “power mad", adding "his Zionist friends no doubt want a Zionist in charge because they put Israel above The Left or even Britain”.
Another, from an account in the name of @coo1_Daddy said: ”This is further proof that stalking horse #Lansman is a fraud and is only using @PeoplesMomentum as a vehicle to further his own Zionist takeover of the Labour party after McNicol, even if this lets in another right winger.”
Mr Lansman has previously expressed his support for pro-Palestinian causes and has criticised organisations such as Labour Friends of Israel over an alleged failure to criticise Israeli actions.
In a statement, Ms Formby said: “Just seen antisemitic attacks on @jonlansman. They are disgraceful and must stop. This sort of abuse has no place in the Labour Party.”
Media commentator Nick Cohen also condemned the attacks on Mr Lansman, saying: "On the far left, Jewishness is irrelevant if you are loyal and a total explanation of your character if you speak out. It is irrelevant one minute and everything the next."
The new general secretary will be elected by Labour’s governing body, the national executive committee, later this month. The vacancy was caused by the resignation of Iain McNicol.