Polanski was speaking to the BBC on the day before polls open for elections in Scotland, Wales and England.
The Green Party is hoping to make gains, particularly in urban areas where they are challenging traditional Labour strongholds.
However, during the campaign some of the party’s candidates have been accused of making antisemitic comments.
Polanski said their messages were “unacceptable” and that the party would be implementing a “standardised vetting process” in the future as well as mandatory training for candidates “to make it clear that antisemitism is completely unwelcome” in the party.
“It is also important to say one case of antisemitism is one too many. This is a handful of cases and actually we have over 4,500 candidates, the vast, vast majority of which are doing amazing work in their communities right now,” he added.
Polanski was also asked about a row that began last week, when he shared a social media post criticising the police response to the Golders Green attack.
The message on X accused the officers, who had arrested the suspect, of “repeatedly and violently kicking a mentally ill man in the head when he was already incapacitated by Taser”.
Met Police chief Mark Rowley accused Polanski of amplifying “inaccurate and misinformed commentary” and Polanski later apologised for “sharing a tweet in haste”.
Reflecting on his response, Polanski told the BBC that police officers “can be incredibly brave when they run towards the scenes of crimes” but also that he had been “traumatised” by seeing the footage.