Despite all the accumulating evidence, some circumstantial, some more telling, I had always tried to give Corbyn the benefit of the doubt. His understandable passion for the plight of the Palestinian people, and anger at the actions of Israeli governments might boil over into inadvertent – and that is an indulgent word for it – antisemitism, as is the case with so many on the left.

Either through intellectual laziness or ignorance or carelessness – inadequate excuses, but explanations all the same – they might have confused indignations about Netanyahu or anti-Zionism with antisemitism. They probably haven’t read much history, poor things. A little education might do them some good.

It was a little bit of a mystery as to why the Labour Party’s disciplinary procedures were so painfully slow, but then it is a bureaucracy, after all. The Chakrabarti Report into antisemitism in the party was a cynical disgrace, but then politics is like that isn’t it? And she is herself a doughty campaigner for human rights. Shami Chakrabarti was nominated by Corbyn for the House of Lords shortly after her complacent investigations were completed, with little further action.

It is a report that stands out in its refusal to recognise antisemitism as a unique phenomenon, and not simply a subset of racism. Her terms of reference were carefully set to enquire into “antisemitism and other forms of racism, including Islamophobia”. See the skilful elision there? She refused to acknowledge the peculiar aspects and history of antisemitism thus: “There is not, and cannot be, any hierarchy of racism.” Hopeless. But, as I say, politics is like that.

Perhaps, too, Labour’s refusal to accept the International Holocaust Alliance's working definition of antisemitism was simply a matter of pride, wanting to say things in their own words. Corbyn reportedly had a particular problem with the bit about “claiming that the existence of a state of Israel is a racist endeavour”. He, maybe, wanted to be able to do that, based on his reading of the events of 1948, presumably. On the other hand, I don’t know what he thinks about the catastrophe/war of independence specifically, because no one’s yet asked him, or, if they have, the answer hasn’t been so self-condemnatory as to make the headlines.

Should I vote Labour? Corbyn's biggest policies explained Show all 9 1 / 9 Should I vote Labour? Corbyn's biggest policies explained Should I vote Labour? Corbyn's biggest policies explained Brexit Labour is committed to leaving the European Union but would have different negotiating priorities to the Conservatives. It has said it would have a “strong emphasis” on staying in the single market and the customs union. German Chancellor Angela Merkel and leading figures in Brussels have been unambiguous that membership of the single market is impossible without free movement. PA Should I vote Labour? Corbyn's biggest policies explained Immigration The party would drop “bogus immigration targets” but move to a managed system of migration favoured by many leave voters. It has said this “may include employer sponsorship, work permits, visa regulations or a tailored mix of all these”. Getty Should I vote Labour? Corbyn's biggest policies explained The Economy Labour’s manifesto commits to balance government spending with the amount raised by taxation, which can mean little more than significant tax increases. The greatest burden will fall on higher earners but they cannot meet demand on their own. It has also promised to bring rail companies back in to public ownership and cap fares. The party would also renationalise Royal Mail. It also promises a “transition” to publicly owned energy. Peter Byrne/PA Should I vote Labour? Corbyn's biggest policies explained Tax No one earning under £80,000 would pay any more in national insurance or income tax. It would raise corporation tax, from the current low of 19p to 26p. This higher rate would still be a competitive internationally, but the government is currently fighting hard to attract business in the wake of Brexit and they say a low corporation tax rate is crucial. Labour would also lower the top, 45p income tax threshold to £80,000. In theory, this could raise £7bn, but only if higher earnings did not decide to move abroad. Reuters Should I vote Labour? Corbyn's biggest policies explained NHS Labour has promised more money for GP services, free hospital parking for patients, staff and visitors, and to take a million people off NHS waiting lists by guaranteeing treatment within eighteen weeks. These promises will be expensive to keep, and there is no certainty that the party’ s commitment to raising taxes on higher earners, increasing capital gains tax and reversing cuts to corporation tax will be enough to meet the need. PA Should I vote Labour? Corbyn's biggest policies explained Education The party has pledged to abolish university tuition fees and reintroduce maintenance grants and give free school meals to all schoolchildren. PA Should I vote Labour? Corbyn's biggest policies explained Housing Labour’s manifesto commits to building 1m new homes, and would introduce controls on rent rises for private renters. It would also scrap the so-called bedroom tax. Getty Should I vote Labour? Corbyn's biggest policies explained Environment Labour would ban fracking, but, crucially, also supports new nuclear projects. It would also introduce a new Clean Air Act to deal with illegal air quality Getty Should I vote Labour? Corbyn's biggest policies explained Defence Its manifesto says it is committed to the NATO target of 2 per cent spending on defence. It is also committed to the renewal of Trident, even though Jeremy Corbyn has spent a lifetime campaigning against it. AFP/Getty Images

When you start to add it all up, though, you do start to wonder what’s going on in his head. Particularly, you wonder whether, in fact, all Corbyn’s political prejudices – against American “imperialism”, Nato as an “occupying force”, about international finance capitalism, for Hezbollah and Hamas – are just fanning out, or feeding in, to one unifying theme: an unacknowledged antisemitism. The best that can be said is that he is so dim he probably doesn’t even realise it, but that may be too generous.

Now I am not so sure even about that. Yes, we have reached a tipping point. The foreword he wrote, only a few years ago, to Imperialism: A Study by JA Hobson (first published in 1902) endorsing this “great tome” is as damaging as any of the rest of the revelations that have emerged because it endorses this old trope about the international conspiracy.

The relevant passage in Hobson’s critique of imperialism, one that inspired Lenin, concerns the “pressures” that drove the British and others to acquire their colonies and subjugate their peoples, the forces of international capitalism, controlled “by men of a single and peculiar race, who have behind them many centuries of financial experience … in a unique position to control the policy of nations”. I don’t think he was talking about the Irish.

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Apparently, in intellectual lefty circles this slight problem with JA Hobson is well known. In fact, a quick glance at Wikipedia tells us: “While not as antisemitic as his previous books, Imperialism includes an accusation that there is an international conspiracy of Jewish financiers.” In an earlier work, concerning the Boer War, Hobson was even more explicit about who he blamed for it: “a small group of international financiers, chiefly German in origin and Jewish in race”.

Hobson, then, is the intellectual granddaddy of Corbyn's half-baked conspiracy theories about Wall Street and capitalism, and, thus, his antipathy to the European Union, which he has always thought of as a bosses’ club inimical to state socialism. As Keynes once remarked: “Practical men who believe themselves to be quite exempt from any intellectual influence are usually the slaves of some defunct economist.” And, in vulgarised and still more aggressive terms, the notion of the international Zionist conspiracy sustains all the Twitter Jew-haters who send their mad, upsetting messages to the likes of Luciana Berger.

It also seems to infect all those in the top reaches of the Labour Party who display unforgivable apathy towards what is going on in their ranks. They have been taking the notion of “no enemies on the left” to an absurd and dangerous extreme. It seems to have occurred to none of them that they really have, literally unthinkingly, adopted the premises that led to the Nazis and the Holocaust. Yet they wonder why Jewish people get upset.

Even if I were not now convinced that Corbyn is an antisemite, if not a particularly sophisticated or clever one, I would still be highly disturbed by his distorted view of the world. Writing a foreword to a dusty old work of eccentric economics is the rough equivalent of talking to oneself in the bath, but now we come to overhear the words they are quite astonishing.

Here they are, in all their pretentious grandeur, just in case you were curious about what philosophical underpinnings will lie beneath a Corbyn government: “The big imperial force has been the United States on behalf of global capitalism and the biggest mostly US-based corporations”. Obviously Jeremy has never heard of Volkswagen, Huawei or Softbank. The future leader of the opposition goes on: “Thus the Cold War was followed by American media and cultural values, in an attempt to create an empire of the mind.” That’ll explain The Simpsons, then.

As I say, thanks to the efforts of the likes of Tom Watson, and journalists such as Stephen Pollard, editor of the Jewish Chronicle, and the equally estimable Danny Finkelstein of The Times, we are learning more about Labour and, now, this especially feeble artefact of Corbyn’s ideology. Many of us might have been inclined to give the poor old fool, the last of the Bennites, the benefit of the doubt before. He has, as everyone does acknowledge, spent a life-time campaigning against racism, getting himself arrested outside South Africa House in Trafalgar Square protesting about apartheid, and all the rest of it.