Jeremy Corbyn has claimed Labour anti-Semitism was "dramatically overstated for political reasons" as he offered no apology for findings the party broke equality law.
The Equality and Human Rights Commission today found Labour committed three breaches of the civil law Equality Act under Mr Corbyn's leadership.
The long-awaited report found unlawful "political interference" from Mr Corbyn's office staff in 23 complaints - including one against the leader himself.
Yet Corbyn today said "I do not accept" all the EHRC's findings and said "my team acted to speed up, not hinder the process."
Offering no apology in a defiant 270-word statement, he said "of course" there is anti-Semitism in the party but turned his fire on "opponents" and the media for exaggerating the problem.
“One antisemite is one too many, but the scale of the problem was also dramatically overstated for political reasons by our opponents inside and outside the party, as well as by much of the media," he wrote.
"That combination hurt Jewish people and must never be repeated."
Mr Corbyn's wife, Laura Alvarez, went further tweeting: "PLEASE BOYCOTT THE POISON MAINSTREAM MEDIA AND STAND WITH THE BEST INTERNATIONAL LEADER AND ANTI RACIST ACTIVIST! CHECK FACTS!"
Sir Keir told a press conference: "If after all the pain all the grief and all the evidence in this report, there are still those who think there’s no problem with anti-Semitism in the Labour Party, that it’s all exaggerated or a factional attack, then frankly you are part of the problem too - and you should be nowhere near the Labour Party either."
Asked directly if he was saying Mr Corbyn didn't belong in Labour, Sir Keir said ”I’ll look carefully at what Jeremy Corbyn has said in full," but added: "Those who deny there’s a problem are part of the problem."
Asked if he’d reopen cases involving Mr Corbyn himself, Sir Keir replied: “We’ll look at all cases.”
However, the new leader stopped short of saying he would take action directly against his predecessor.
Alasdair Henderson, Board member lead for the investigation at the EHRC, said Mr Corbyn's claim that his team acted to speed up the process was valid, but still undermined the process.
In his statement, Mr Corbyn insisted "antisemitism is absolutely abhorrent, wrong and responsible for some of humanity’s greatest crimes".
He added: "My sincere hope is that relations with Jewish communities can be rebuilt and those fears overcome. While I do not accept all of its findings, I trust its recommendations will be swiftly implemented to help move on from this period."
Today's 130-page report did not find personal anti-Semitism on the part of Jeremy Corbyn. No criminal law was broken by Labour.
But it found Labour was responsible for three civil law breaches of the Equality Act:
The report found unlawful political interference in anti-Semitism complaints “throughout the period of the investigation”. In a sample of 70 complaint files, investigators found "23 instances of political interference by LOTO (Leader of the Opposition) staff and others.”
That included a complaint against Jeremy Corbyn himself over an anti-Semitic mural he had commented on in 2012.
In March 2018 Mr Corbyn expressed “sincere regret” for objecting on Facebook, in 2012, to the removal of a mural which showed hook-nosed figures playing Monopoly on the backs of naked men.
The then-leader said he had not looked closely at the mural and therefore did not realise it was anti-Semitic.
In an email, his office's staff said the complaint should be dismissed because it "seems to fall well below the threshold required for investigation".
The EHRC's interim chair Caroline Waters said there had been "inexcusable" failures which "appeared to be a result of a lack of willingness to tackle anti-Semitism rather than an inability to do so". The report found "serious failings in leadership".
The report also found Labour committed “unlawful harassment" due to the actions of two "agents" - one of whom is former mayor of London Ken Livingstone.
The ex-mayor accused ‘the Israel lobby’ of a smear campaign to stigmatise critics of Israel as anti-Semitic, the EHRC said. The watchdog today found his comments were "anti-Semitic" and "had the effect of harassing Labour Party members" - and Labour was responsible for them because Mr Livingstone was a high-profile party figure.
His statements “had the effect of creating an intimidating, hostile, degrading, humiliating or offensive environment for members, and prospective members, of the Labour Party, particularly those who were Jewish", the EHRC added.
His case appeared to be one of those interfered with by the leader’s office, the EHRC revealed. “There is evidence of LOTO staff being directly involved in the decision to investigate the second complaint of antisemitism made against Ken Livingstone,” the watchdog said.
Sir Keir today praised the "comprehensive, rigorous and professional" report for uncovering unlawful acts, declaring: "The report’s conclusions are clear and stark. They leave no room for equivocation."
Vowing to implement all its recommendations in full, including an independent complaints process, Sir Keir added: "I found this report hard to read and it is a day of shame for the Labour Party.
"We have failed Jewish people, our members and the British public. And so on behalf of the Labour Party, I am truly sorry for all the pain and grief that has been caused."
Jeremy Corbyn's statement in full
“Antisemitism is absolutely abhorrent, wrong and responsible for some of humanity’s greatest crimes. As Leader of the Labour Party I was always determined to eliminate all forms of racism and root out the cancer of antisemitism. I have campaigned in support of Jewish people and communities my entire life and I will continue to do so.
“The EHRC’s report shows that when I became Labour leader in 2015, the Party’s processes for handling complaints were not fit for purpose. Reform was then stalled by an obstructive party bureaucracy. But from 2018, Jennie Formby and a new NEC that supported my leadership made substantial improvements, making it much easier and swifter to remove antisemites. My team acted to speed up, not hinder the process.
“Anyone claiming there is no antisemitism in the Labour Party is wrong. Of course there is, as there is throughout society, and sometimes it is voiced by people who think of themselves as on the left.
“Jewish members of our party and the wider community were right to expect us to deal with it, and I regret that it took longer to deliver that change than it should.
“One antisemite is one too many, but the scale of the problem was also dramatically overstated for political reasons by our opponents inside and outside the party, as well as by much of the media. That combination hurt Jewish people and must never be repeated.
“My sincere hope is that relations with Jewish communities can be rebuilt and those fears overcome. While I do not accept all of its findings, I trust its recommendations will be swiftly implemented to help move on from this period.”