Labour's London mayoral candidate Sadiq Kahn has indicated that the party's mishandling of the anti-Semitism row could harm his chances at the polls.
The former-minister, who is seen as Labour's best hope of a positive result in elections across the UK on Thursday, said the leadership had acted too slowly to tackle concerns about racist views in the ranks.
Mr Kahn told the Observer that the upper echelons of the party needed education and training "as clearly they don't understand what racism is, and there is no hierarchy when it comes to racism".
A poll carried out as the controversy unfolded, gave the Conservatives an eight-point lead and experts tip Labour to lose up to 150 council seats in England and face a hard night in elections to the Scottish and Welsh governments.
The poll, by Opinium for the Observer, showed Labour on 30% to the Conservatives' 38% - with Ukip on 15% and the Liberal Democrats, SNP and Greens all on 5%.
It was based on 2,005 online interviews with UK adults between April 26 - 29.
Jeremy Corbyn has been criticised over his response to highly controversial comments linking Hitler and Zionism by prominent stalwart Ken Livingstone.
Mr Corbyn's attempts to put a lid on the situation by announcing an independent review and tighter procedures was undermined when Mr Livingstone - who has been suspended along with MP Naz Shah - publicly stuck by his comments.
Meanwhile Israel's new ambassador Mark Regev to Britain has said parts of the left were "in denial" about anti-semitism.
He told the Sunday Times: "I have no doubt that part of the left is in denial. They say 'anti-Semitism, that's the right, that's the fascists'. That's a cop-out. It doesn't stand up to serious historical examination."
And the leader of the Labour opposition party in Tel Aviv, Isaac Herzog, said recent events needed to act as a "red alert" that urgent action was required.
In an open letter to his UK counterpart, Mr Herzog said he had been "appalled and outraged by the recent examples of anti-Semitism by senior Labour Party officials in the United Kingdom".
"Knowing that the British Labour Party has a proud and distinguished history of fighting racism in every form, has only added to my profound disappointment at recent events, which must act as a red alert and prompt immediate action," he wrote.