It is not every day that one hears Jeremy Corbyn likened to Enoch Powell. Nor has Lord Sacks, who made the comparison, ever before said anything half so startling about politics.

During three decades in public life, including 22 years from 1991 to 2013 as Chief Rabbi, Jonathan Sacks has striven, like other religious leaders, to refrain from making comments which might be regarded as partisan.

The press can create a story out of a careless remark, but that is not what happened here. In his interview with The New Statesman, Sacks uses language with his usual precision, to build an indictment as deliberate as it is devastating:

“The recently disclosed remarks by Jeremy Corbyn are the most offensive statement made by a senior British politician since Enoch Powell’s 1968 ‘Rivers of Blood’ speech. 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.

“We can only judge Jeremy Corbyn by his words and his actions. He has given support to racists, terrorists and dealers of hate who want to kill Jews and remove from 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 anti-Semitism. 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.”

On Sunday morning, Andrew Marr put it to Sacks that this was nevertheless “over the top”, and Sacks replies that it was, on the contrary, a warning he was obliged to give:

“Anyone who befriends Hamas and Hezbollah is in danger of engulfing Britain in the kind of flames of hatred that have reappeared throughout Europe, and is massively irresponsible.There is a danger that Jeremy Corbyn will one day be Prime Minister.”

Jews, he added, are thinking of leaving Britain. He called on the Labour leader to “repent and recant”, and to “stop the persecution of people within his own party”, in order to “rebuild some very damaged relationships with the Jewish community”.

These remarks are all the more striking when one notes that Sacks is a shy intellectual, who has been reluctant to court controversy, and who, in the words of one close observer, “knows he’s tone deaf to politics”. For him, the question transcends politics, and has become one where it would be immoral to remain silent.

When the Hard Left have become incapable of condemning anti-semitism in their own ranks, or of seeing how far Corbyn has gone astray, an attempt must be made to shake them out of their complacency.

Sacks was born to Jewish parents in London in 1948. His father, who had arrived from Poland at the age of two, sold cloth in Commercial Road in the East End. His mother, who was born here, worked in her family’s wine shop.

Jonathan, the oldest of four brothers, was educated at Christ’s College, Finchley, in those days a grammar school. About half the pupils were Jewish, and its old boys include Lord Young of Graffham, Sir Peter Strawson, Charles Saatchi and Will Self.

On one occasion, Jonathan went to see his local MP for help with a piece of school work. She was called Margaret Thatcher:

“I was doing an essay on proportional representation once and I went to her – I’m 17 years old – she looks at me and says” – he leans forward with narrowed eyes and breaks into a high-pitched imitation of his former MP – “you’re not a liberal, are you?’”

From Finchley, he proceeded to Gonville and Caius College, Cambridge, to read Moral Sciences, or philosophy, in which he took a First. His hero, Wittgenstein, had until a few years earlier been at Trinity College, which is next door. When Sacks appeared on Desert Island Discs, he described the impact of Cambridge:

“It was stunning, it was sensational, it was the pulse of the place. It wasn’t so much the timeless beauty, though I loved that as well, but the sheer pulse of so many people with so many ideas. I found that very exciting.”

On the same programme he said: “My great ambition in life was to be an accountant.” He married young, to Elaine Taylor, then a physiotherapist, and they went on to have three children. But his life had been changed in 1967 by the Six-Day War, when several Arab countries tried to drive Israel into the sea: “It looked as if a second unthinkable Holocaust was about to take place.”

Israel instead won a tremendous victory, and a seed had been planted in his mind, which some years later was to germinate. Although he continued with post-graduate philosophical studies, he also became increasingly interested in Judaism, felt mystic longings and attended a seminary in Israel, after which he qualified in London as a rabbi, and worked at Golders Green and Marble Arch synagogues.

His career is in some ways comparable to that of Justin Welby, the present Archbishop of Canterbury, who likewise displayed no particular piety as a child, and did not immediately go in to the Church, but almost as soon as he did, was marked out for rapid promotion.

In 1991, Sacks with declared reluctance became Chief Rabbi, a post in many ways as unenviable as being Archbishop, Jews being at least as divided and quarrelsome among themselves as Christians are inclined to be, a point on which I touched in an earlier profile for ConHome.

D.D.Guttenplan, Editor of Jewish Quarterly and a Labour Party member, told me while I was writing this piece that the comparison between Corbyn and Powell was quite misplaced, because whereas when the latter was speaking, there was deep hostility towards immigrants from the Caribbean, Jews who have long lived in Britain do not now feel threatened:

“Jonathan Sacks seldom spoke for me when he was Chief Rabbi and he doesn’t speak for me now. Jews don’t have a Pope and we don’t have a Pope for a reason – you know the joke, two Jews, three opinions.

“On this particular issue he’s clearly lost his sense of proportion if not his mind.

“I do think Jeremy Corbyn has caused offence and hurt and should apologise. What he was saying was very hurtful, but entirely unthreatening. To feel disregarded is painful, but it’s not the same as feeling threatened.”

Sacks has demonstrated, in numerous books, lectures and episodes of Thought For The Day, and in his series Morality in the 21st Century, now playing on Radio Four, a tremendous gift for philosophical exposition. But in his first address as Chief Rabbi, he insisted that religion must come first:

“We have become secularised. There are times when we believe that Jews can survive without beliefs, as an ethnic group sustained on nostalgia. But faith is not a luxury we can live without.”

How does one conduct oneself as a religious leader in a society which has become more secular? Sacks remained on excellent terms with all four Prime Ministers – John Major, Tony Blair, Gordon Brown (with whom his latest intervention appears to have been coordinated) and David Cameron – during his term of office as Chief Rabbi.

He has also shown his appreciation of thinkers such as his first doctoral supervisor, Bernard Williams, who dismissed religion and “regarded as incoherent the idea of a God who is above space and time and yet communicates with us who live in space and time”:

“I learnt much from his work. He taught us that the wish to be someone else was a contradiction in terms. As one of the Jewish mystics, Zushya of Hanipol, put it: ‘When I get to Heaven, they will not ask me, “Zushya, why weren’t you Moses?’” They will ask me, “Zushya, why weren’t you Zushya?”‘”

In his attack on Corbyn, Sacks in a profound way is being Sacks, defending his religion against attack. The problem is that Corbyn will go on being Corbyn.