The former London Mayor had already been suspended for two years for previous comments.
The emails were reportedly leaked by a former party official who was motivated to “expose failing in the compliance unit’s response to antisemitism complaints before Jennie Formby became general secretary” in April 2018.
The source said: “These emails show Labour’s compliance unit prior to Jennie Formby taking over failed to suspend members who had made appalling antisemitic remarks for over a year, despite clear evidence and repeated attempts by colleagues and complainants to seek action.
“It is completely unacceptable that it took so long for the compliance unit to suspend members who had defended the blackshirts and suggested the Holocaust was a hoax.
“It should have been immediately clear that these cases merited suspensions.”
A Labour Party spokesperson said: "The Labour Party takes all complaints of antisemitism extremely seriously and we are committed to challenging and campaigning against it in all its forms.”
A Labour source added that since becoming general secretary, Ms Formby has “sped up” the process for dealing with antisemitism complaints.
Between April 2018 and January 2019, 96 members were handed suspensions, and a further 12 have been expelled.
