My heart sank. My work colleague — the one responsible for human resources — dumped a lengthy tome onto my desk with the words: “Employee Handbook: Document for your approval” emblazoned across the front cover. He’d been reviewing our internal policies and procedures for months, and now I had to read and sign off on it. I know some people love this stuff, but personally, I’d prefer to mire myself in antisemitic drivel than suffer this kind of pain any day.

Turning to page 497 — at least that’s how it felt — I reached the section on harassment and bullying. And buried deep in yet another incomprehensibly dull paragraph came this little gem: “It should be noted that it is the impact of the behaviour which is relevant and not the motive or intent behind it.”

Beyond all the rancour at the moment, there’s an important philosophical debate about how contemporary antisemitism is defined. Which is more important: the experience of the victim or the motivation of the perpetrator? Like our staff handbook, the MacPherson definition of racism clearly leans towards the former, but in reality, it’s rarely straightforward. There is a distinction to be drawn between something done with deliberate intent to harm and something done accidentally or unknowingly. We even find it in the text of al chet which we’ll read shortly on Yom Kippur. “For the sin we have committed before You willingly” and “for the sin we have committed before You inadvertently”. Both are sins, but one can distinguish between them.

Last year, working with the Community Security Trust, JPR published an extensive report on attitudes towards Jews and Israel among the population of Great Britain. Our starting point was to only measure the types of attitudes most Jews experience as antisemitic.

We had done empirical work on this previously, so we could apply a standard rule: where more than half of the British Jewish population regards a particular notion to be at least “probably” antisemitic, if not “definitely so”, we would include it. Where it didn’t reach this threshold, we would exclude it. Thus every statement tested in that study could be deemed antisemitic if based on the principle of “the impact of the behaviour”.

But we wanted to go further. We wanted to investigate underlying motives to see if there is any evidence of anti-Jewish sentiment among those expressing the types of extreme anti-Israel views most Jews experience as antisemitic. Views like Israel is “committing mass murder in Palestine”, or “deliberately trying to wipe out the Palestinian population”, or “the cause of all the troubles in the Middle East”.

We found that there is. The more people agree with these types of ideas, the more likely they are also to agree with standard anti-Jewish tropes, for example around superiority, dual loyalty and nefarious use of power. An anti-Jewish motivation is not always evident, but the probability that it is present increases the more anti-Israel views are in evidence. This is true not only of the population of Great Britain in general, but of all sub-groups too, including, most importantly at the moment, the self-identifying far-left.

In the vitriol that has accompanied the discussions about antisemitism in the Labour Party, some leftists have used our findings to argue that the far-right is much more antisemitic than the far-left. If we focus only on traditional anti-Jewish tropes, they are right. But they deliberately ignore the data demonstrating that the far-left significantly outscores the far-right on extreme anti-Israel attitudes. Critically, about four in five far-leftists hold at least one anti-Israel view that most Jews are likely to experience as antisemitic. And close to a quarter of all far-leftists hold multiple extreme anti-Israel views which correlate strongly with traditional anti-Jewish sentiment.

If we apply the principles of bullying or harassment in the workplace — ie the impact of the behaviour — there is little question that Jeremy Corbyn’s Labour Party has a serious antisemitism problem. But even if we apply the more stringent principle of underlying motive or intent, we reach much the same conclusion. The far-left does antisemitism somewhat differently from the far-right, but empirically, there’s no question: often if not always, buried beneath its supposedly legitimate critiques of Israel are all manner of antisemitic sins.

Jonathan Boyd is executive director of the Institute for Jewish Policy Research (JPR)