Jonathan Sacks made the most outspoken attack yet on the Labour leader, branding him “an antisemite” who has “given support to racists, terrorists and dealers of hate”.
“It was divisive, hateful and, like Powell’s speech, it undermines the existence of an entire group of British citizens by depicting them as essentially alien,” Lord Sacks said.
The condemnation deepens the crisis that has engulfed Mr Corbyn since his remarks at a pro-Palestinian event five years ago emerged last week.
He criticised “Zionists” who “don’t want to study history, and secondly, having lived in this country for a very long time, probably all their lives, don’t understand English irony either”.
Some Labour MPs reacted with horror, while Helen Grant, the Conservative MP, reported him to the parliamentary standards watchdog.
Now Mr Sacks has described the words as “the most offensive statement made by a senior British politician since Enoch Powell’s 1968 ‘Rivers of Blood’ speech”.
“We can only judge Jeremy Corbyn by his words and his actions,” he told the New Statesman magazine.
“He has given support to racists, terrorists and dealers of hate who want to kill Jews and remove Israel from the map.
“When he implies that, however long they have lived here, Jews are not fully British, he is using the language of classic pre-war European antisemitism.”
Mr Corbyn has defended his comments, insisting that he was referring to a specific group of “pro-Israel activists” and had not used the term Zionist as a “euphemism” for Jewish people.
He claimed he was “now more careful with how I might use the term ‘Zionist’ because a once self-identifying political term has been increasingly hijacked by antisemites as code for Jews”.
But Lord Sacks added: “When challenged with such facts, the evidence for which is before our eyes, first he denies, then he equivocates, then he obfuscates.
“This is low, dishonest and dangerous. He has legitimised the public expression of hate, and where he leads, others will follow.
In response, a Labour Party spokesperson said: “This comparison with the race-baiting Enoch Powell is absurd and offensive.
“Jeremy Corbyn described a particular group of pro-Israel activists as Zionists, in the accurate political sense – not as a synonym or code for Jewish people.
“Jeremy Corbyn is determined to tackle antisemitism both within the Labour Party and in wider society, and the Labour Party is committed to rebuilding trust with the Jewish community.”
Labour has been dogged by allegations of antisemitism all summer, sparked by a refusal to fully implement the International Holocaust Remembrance Alliance's (IHRA) examples to define antisemitism.
Mr Corbyn and his key advisers have resisted including any statement that says that claiming the Israeli state is a "a racist endeavour" is "denying the Jewish people their right to self-determination".
A meeting of the party's ruling national executive committee next week is expected to finally force Mr Corbyn to step into line with the wishes of his MPs.
However, critics fear the implementation of the IHRA definition and examples will be done in a way to prevent disciplinary action against anyone who breached the IHRA examples in the past.
That would protect the likes of Mr Corbyn and Seumas Milne, his closest aide, from the risk of being investigated for their historical comments.
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