I am not— let’s make this clear right at the beginning — a personal friend of the Chief Rabbi. I do not go to his house for Friday-night dinner, or indeed at any time nor do we hang out at the pub. We have never played golf, nor gone shopping together, and neither have we ever watched Strictly Come Dancing after Shabbat goes out.

Yet I feel extremely confident in my limited knowledge of the Chief Rabbi’s lifestyle to be able to say, loud and clear, that he is not, and never has been, a close personal friend of Boris Johnson. And I found myself saying this on social media over and over again last week, as Labour-supporting, non-Jewish (and some Jewish) contacts reacted to his statement about Labour Party antisemitism.

“Well, what do you expect,” was a typical comment. “Of course the Chief Rabbi is telling people to vote Conservative. After all, he’s a big mate of Boris Johnson.” (He wasn’t, by the way).

At first I was baffled. What on earth did they mean? Anyone who knows anything about Rabbi Mirvis would surely realise that his concern for the underdog, his campaigns on subjects such as modern slavery, not to mention his moral standing and attachment to basic Jewish values such as the Ten Commandments, would make him an unlikely confidant of the blond buffoon.

In fact, were it not for the virulent antisemitism, one could imagine Rabbi Mirvis’s political sympathies being rather more left-leaning. He’s conservative, sure, that comes with Orthodoxy, but he’s no right-wing populist.

But then those Facebook experts provided — triumphantly in some cases — the evidence. “He says so himself” they wrote, posting the statement that the Chief Rabbi’s office put out when Mr Johnson was appointed leader of the Conservative Party.

It read: “I am delighted to congratulate Boris Johnson, a longstanding friend and champion of the Jewish community, on becoming the next leader of the Conservative Party and our next Prime Minister. As he accepts upon himself the mantle of responsibility to lead our nation, may he be blessed with the wisdom to successfully navigate the political uncertainties we face and bring healing and prosperity to our great country.”

Now this statement is not difficult to unpack, for insiders. “A longstanding friend and champion of the Jewish community” means “someone who has mostly managed to avoid antisemitism in public, and has never called for Israel’s destruction”. The mentions of “responsibility” and “wisdom” might suggest these attributes are in short supply, so many heartfelt prayers will be needed to achieve the near miracle of the hoped-for “healing and prosperity”.

But, on social media, the statement might as well have ended at the word “friend”. Patiently (and through gritted teeth), I pointed out the vital lack of a comma before that “and”. With a comma — yes, personal friend. Without a comma — nope, just another politician.

But it was hard to persuade people. They really wanted it to be true. They wanted to believe in this mythical friendship, because that meant they could shrug off the moral question that the Chief Rabbi was posing. So they were willing to believe that the most senior rabbi of the main Orthodox group in the UK would use the things that Jewish people fear the most — persecution, racism, hatred — to help a mate win an election. In other words, manipulative, lying, cynical exaggeration. A quite breathtaking insult, straight from the playbook of antisemitic tropes, although I really believe that none of them stopped long enough to think through the implications of their words. Such is social media. Such is underlying prejudice.

But anyway, they said. There was another reason to discount the Chief Rabbi’s words. He hardly represents any Jews at all! Children’s writer Michael Rosen said so in a column in the Morning Star, which argued that half of the Jews in the UK aren’t synagogue members, and so no rabbi, however chief, can be said to represent British Jews. The obvious counter to this — that even if Rabbi Mirvis speaks only for himself, he still knows more about the Jewish community and its fears than Michael Rosen — fell on deaf ears.

In the same week, comedy writer Sara Gibbs wrote a long, detailed analysis of Labour antisemitism. When I shared it, one contact posted “I prefer Noam Chomsky”. Chomsky’s support for Corbyn is unsurprisingly lacking in detail or nuance. But another dear friend thanked me, and Sara, for explaining what Zionism actually means. “I know that in the past I have probably repeated antisemitic sentiments without even being wholly aware that I was. But I continue to learn.”

So, it is worth it after all — the posting and explaining and gritting of teeth. But perhaps we could quietly retire the phrase “friend of the Jewish community” from now on.