A little over three years ago, shortly before Jeremy Corbyn became leader of the Labour Party, this newspaper set out seven questions for him to answer regarding people and organisations who he had supported, assisted or spoken alongside. It was a gruesome list of terrorists, Holocaust deniers and antisemites, and it was vital and urgent for Mr Corbyn to answer these questions satisfactorily, the JC urged, lest he “be regarded from the day of his election as an enemy of Britain’s Jewish community”.

Nevertheless, cautioned the writer of that editorial, “there is no direct evidence that he has an issue himself with Jews”. This was a question of who Mr Corbyn associates with and the causes he promotes, rather than his own personal attitudes or prejudices.

Three years on, that initial warning seems prescient; but the benefit of the doubt extended to Mr Corbyn personally has long run out. This is one reason why the new edition of my book, The Left’s Jewish Problem: Jeremy Corbyn, Israel and Antisemitism, published last week, has a more pessimistic outlook than the original version that came out in 2016.

Back then, it was possible to plot a way for a Corbyn-led Labour Party to navigate its way out of this problem. If the party leadership accepted that the antisemitism amongst its members was not just the result of random prejudice or ill-chosen language, but the product of a political mindset, then there was scope for the change that was necessary to turn around what was already a mounting problem.

If people at all levels in Mr Corbyn’s party, from the leadership to the grassroots, could take complaints of antisemitism seriously instead of dismissing them as smears designed to silence critics of Israel, then common ground could be found in understanding the particular nature of left wing antisemitism and taking steps to tackle it.

If other opinion formers on the left, including influential voices in the broader movement that propelled Corbyn to the leadership, led a process of learning and engagement with the Jewish community, and if those who attacked the community were vigorously and consistently called out for it, that might provide a platform for the party to rebuild its relationship with British Jews.

Instead, Labour has zigzagged from one false step to another, like a pinball bouncing its way towards the hole marked “Game Over”. From Oxford University Labour Club, to the supressed Royall Report, the Chakrabarti whitewash, the failure — twice! — to expel Ken Livingstone, the chronic failings of its disciplinary processes, and political interference at the highest levels to avoid taking action. Throughout all of this, we witnessed a constant stream of antisemitic statements, posts, tweets and comments from Labour Party members, councillors, activists and officials, past and present, all the while dismissed by Mr Corbyn’s most loyal supporters on social media and in party meetings as smears and lies invented by a coalition of Zionists, Tories and Blairites to keep Britain from reaching its socialist utopia.

Then there is Mr Corbyn’s own contribution to this sorry tale: his support for the antisemitic mural, his affection for the “brothers” of Hamas, his conspiracy theory about “the hand of Israel” being behind jihadist terrorism in Egypt, his backing for a campaign to rename Holocaust Memorial Day, his wreath-laying, his excuses and evasions and, most damning of all, his haughty, knowing comment that “Zionists” do not understand English irony, even if they — we — have lived in this country all our lives.

Two years ago, most opinion columns about antisemitism in the Labour Party stressed that nobody accused Mr Corbyn himself of being antisemitic; his flaw was that he just did not recognise it, he did not think left-wing people were capable of it, or he had not taken the necessary action to deal with it.

There are not many columnists saying that now. Mr Corbyn may or may not be an antisemite, but he has certainly said and done some things that can reasonably be described as antisemitic.

The other thing that has changed in the two years between the first and second editions of my book is that an antisemitic political culture has taken root in the grassroots of the left-wing movement on which Mr Corbyn’s project depends.

This culture can be found in the Facebook groups that bear Mr Corbyn’s name and the alt-left, new media blogs that count as news sources for his more devoted supporters. Some of these Facebook groups have tens of thousands of members, and websites like The Canary, Novara Media and Skwawkbox have a direct line to the party leadership and are more trusted by Mr Corbyn’s supporters than most national newspapers.

This does not mean that every Corbyn supporter, every member of these Facebook groups, or every writer for these websites, is antisemitic. Far from it. Most, like the rest of the country, are not interested in Jews, Israel or antisemitism. But whenever those subjects are discussed in these forums, the dominant view is that Israel is an apartheid or Nazi state, Zionists are deceitful, manipulative racists, and anyone who complains about antisemitism in Labour is, frankly, a liar and a political enemy.

Add in Twitter and certain Facebook groups with their regular conspiracy theories about the Rothschilds, claims that Israel is behind Isis terrorism and even the occasional Holocaust-denying post, and you have an antisemitic political culture that has nothing to do with ordinary criticism of Israeli policies.

Back in March, when the Jewish community demonstrated outside Parliament to protest about Labour antisemitism, Mr Corbyn accepted for the first time that this was a significant problem. The left has its own forms of antisemitism, he wrote, that should not be “dismissed as simply a matter of a few bad apples”. Momentum, the activist movement that organises Mr Corbyn’s foot soldiers, agreed. “Accusations of antisemitism,” they said, “should not and cannot be dismissed simply as right-wing smears nor as the result of conspiracies.”

But their followers were not listening.

Some Labour MPs who attended the community demonstration were abused on social media and threatened with deselection.

The Facebook pages of The Canary and Skwawkbox filled up with comments about “More ridiculous, vile and false antisemitism smears”, “Wealthy Jewish [sic] prepared to slander Corbyn”, “This is about the illuminati/world bankers/Rothschild’s [sic] who happen to majority Jewish [sic] and happens to be true of what is happening to our planet”, “Zionists run the BBC”, “This is what happen’s [sic] when Zionist Jews control our government!”, and so on.

Some in the leadership of the Labour Party and Momentum now understand that they have lost control of what their supporters think about Jews and “Zionists”. The worry is that it is too late.

One consequence is that Jewish Labour members increasingly find their local party meetings intolerable. An obsession with Israel, expressed in the most extreme, hateful terms, and the assumption that any talk of antisemitism is an anti-Corbyn trick, has persuaded many that it is time to leave.

It is hard to avoid the conclusion that Labour is now institutionally antisemitic. This is an alarming situation for all British Jews, whether they support Labour or not. But for Labour, the party that once enjoyed the support of the vast majority of British Jews, and which prides itself on its anti-racism, it is nothing short of a disgrace.

Dr Dave Rich is author of ‘The Left’s Jewish Problem: Jeremy Corbyn, Israel and Antisemitism’ (Biteback, 2018)