Len McCluskey has said while Labour “never handled the anti-Semitism issue correctly”, some in the party “used” it to undermine Jeremy Corbyn.
The Unite general secretary has thrown his weight behind Rebecca Long-Bailey in the Labour leadership contest.
Speaking to the BBC’s Andrew Marr Show on Sunday morning, McCluskey said the row over anti-Semitism in Labour had provided ammunition for Corbyn’s enemies”.
“I’m absolutely convinced that there were those individuals who opposed Jeremy Corbyn’s election right from the beginning, used the anti-Semitism issue – which I think is quite despicable that they did this on such an important subject – to undermine Corbyn, there’s no doubt about that,” he said.
He added: “Every single anti-Semite in the Labour Party needs to be kicked out.”
McCluskey rejected the accusation Long-Bailey, the shadow business secretary, was simply “continuity Corbyn”.
He said Long-Bailey was “absolutely brilliant”, “completely different” and whose “capabilities are beyond doubt”
“I don’t know she agrees with all his [Corbyn’s] policies, I think she agrees with the radical nature of the alternative that Labour offers the electorate but she’ll have her different views about what her priorities are,” he added.
McCluskey also said Labour’s election loss in December was “virtually, solely down to Brexit”.
Long-Bailey needs the backing of one more Labour affiliate to secure a place on the ballot paper in the contest.
Candidates are required to have won the nomination of three Labour affiliates, including at least two unions, which amount to at least 5% of affiliate members.
The only other route on to the ballot is by receiving nominations from at least 5% of constituency Labour parties (CLPs).
Shadow Brexit secretary Sir Keir Starmer and Wigan MP Lisa Nandy have already made it through the nomination process, and Ms Long-Bailey is widely expected to join them in the coming weeks.
Shadow foreign secretary Emily Thornberry also hopes to be in the final stage of the contest.