The Conservatives have won control of Barnet Council in north London after Labour was punished by voters for the antisemitism controversy.
Barnet, which has one of the UK's largest Jewish populations, was a key target for Jeremy Corbyn's party in the local elections.
Labour was widely expected to win the borough for the first time since the local authority was created in 1964.
London Mayor Sadiq Khan had predicted the party would "probably" claim victory but admitted fears about left-wing antisemitism could damage their campaign.
A defeated Labour councillor in West Hendon, where the Conservatives took all three seats, said that the party's inability with the issue of antisemitism cost them victory in Barnet.
Adam Langleben, who also sits on the national executive committee of Jewish Labour, told the Guardian: "Every Jewish Labour household we visited, people said, “not this time.” Activists were being told, “this is a racist party, an anti-Semitic party”, doors were slammed in their faces.
"The reason we have lost here is the inability to deal with this issue and to tackle antisemitism. The Labour leadership and people around them have seen the signs for a long time and they have not acted."
Mr Langleben called for Jeremy Corbyn to visit Barnet and apologise to the Jewish community.
Labour group leader Barry Rawlings said: "I must say that in some wards where there is a large Jewish community, it has made a difference."
"Of course the Tories did go hard in those areas on that issue, saying that if you vote Labour you're voting for Jeremy Corbyn," added Mr Rawlings.
'"But to be honest most of the conversations have been about potholes rather than antisemitism. That said, we want people to know it is an issue we take very seriously in the Labour Party."
Council leader Richard Cornelius, a Conservative councillor, also said voters were generally more concerned about "local issues" rather than accusations of antisemitism within Labour.
"It's things like potholes, the collection of their rubbish bins and keeping the council tax low," he said.
"Of course there is a concern about anti-Semitism in the Jewish areas, and of course there is a wider concern about more generally - people are horrified, and Labour have to address that.
"It's been very close."
The Conservatives controlled Barnet from 2002 until it fell back into no overall control this March when one of their councillors, Sury Khatri, resigned.
They made concerted efforts to target wards with large Jewish populations in the wake of the controversy convulsing Labour.
The breakthrough came when they took a seat off Labour in Hale ward and all three from the long-time Labour stronghold of West Hendon.
Voter turnout was 43.7% - an increase from 41.1% four years ago.
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