Jeremy Corbyn declined to apologise four times to the Jewish community under questioning from veteran journalist Andrew Neil on Tuesday.
The Labour leader was grilled in a BBC interview about allegations of anti-Semitism within his party following concerns raised by the Chief Rabbi Ephraim Mirvis earlier on Tuesday.
He insisted he has “developed a much stronger process” and had sanctioned and removed members who have been anti-Semitic.
But Mr Corbyn stopped short of apologising despite repeated pressure from Mr Neil.
The Labour leader was challenged over Rabbi Mirvis’s allegation that Labour’s claims it is doing everything to tackle anti-Jewish racism was a “mendacious fiction”.
“No, he’s not right. Because he would have to produce the evidence to say that’s mendacious,” Mr Corbyn replied.
“I’m looking forward to having a discussion with him because I want to hear why he would say such a thing,” he added.
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Mr Corbyn also denied that the blight increased after he took over the party, saying: “It didn’t rise after I became leader.
“Anti-Semitism is there in society, there are a very, very small number of people in the Labour Party that have been sanctioned as a result about their anti-Semitic behaviour.”
“We will not allow anti-Semitism in any form in our society because it is poisonous and divisive, just as much as Islamophobia or far-right racism is,” Mr Corbyn said.
Mr Corbyn insisted he had “strengthened the processes” since a written warning was given to a member who questioned the murder toll of the Holocaust.
Rabbi Mirvis wrote in The Times that Labour’s handling of the issue that has dogged the party under Mr Corbyn’s leadership was “incompatible” with British values.
He said the overwhelming majority of Britain’s Jews were “gripped with anxiety” ahead of the General Election on December 12, warning “the very soul of our nation is at stake”.
Mr Corbyn was also pressed over his plan to broker a “credible” Leave deal with the EU and then be neutral in a referendum along with Remain within six months of taking power.
“I will be the honest broker that will make sure the referendum is fair and make sure that the Leave deal is a credible one,” he said.
“That seems to me actually an adult and sensible way to go forward.”
He also refused to say if he would take out the leader of ISIS, just days after he argued Abu Bakr al-Baghdadi should have been arrested.