A Green council candidate arrested this week over alleged antisemitic social media posts has been seen canvassing subsequently alongside other party members, prompting Labour to say it showed the issue was not being taken seriously by Zack Polanski’s party.

Sabine Mairey was one of two Green candidates in Lambeth, south London, arrested by the Metropolitan police on Thursday morning.

While the Greens declined to comment because of the police inquiry, it is understood that Mairey is being investigated by party officials and is likely to be suspended in the coming days, and that the other candidate, Saiqa Ali, has been suspended.

While Green party rules say candidates under suspension or investigation should not campaign, Mairey was pictured on Sunday campaigning in Clapham, where she is standing, with a group of other party activists.

It is understood that this was not known about by the central party, and that Mairey will be contacted to be reminded of the rules.

Labour said the incident showed a lack of leadership by Polanski, the leader of the Greens in England and Wales. Green officials, however, say it is also a result of a highly decentralised structure, which gives local parties significant power and makes actions like suspending candidates more time-consuming.

Asked about the arrests and other incidents of alleged antisemitism by Green candidates, Polanski, who is Jewish, told BBC One’s Laura Kuenssberg on Sunday programme that this was “not an abstract idea” for him, and that tackling it was hugely important.

“As a Jewish person, those comments disgust me. It’s important that we let the disciplinary process take its place, and that’s exactly what we have,” he said.

He rejected the idea that this was something especially prevalent in the Greens: “I don’t believe we have a particular problem compared [with] wider society and other political parties.”

Polanski said he disowned candidates who had made such comments. Asked if he would “tell people here today: don’t vote for them, they don’t stand for you”, he replied: “That’s right.”

Both women’s names and details have been removed from the page of the Lambeth Greens’ website listing their slate of candidates for Thursday.

Steve Reed, the housing and communities secretary, who was leader of Lambeth council before entering parliament, said: “The Green party is rotting from the head down. Shame on Polanski’s moral cowardice. No apology, no condemnation and no suspension.”