I knew I had it. I had it cold. But what should I do now? I knew the answer to that too, it’s just that I wished I didn’t.

A little more than two months ago, the Times sent me to review the new exhibition at the Jewish Museum. Jews Money Myth it is called. And very good it is too. But as part of my duties I did something which perhaps I wouldn’t have done as a causal visitor. I read the catalogue from beginning to end carefully.

Accompanying plates of many exhibits are first class essays on antisemitism, making it a worthwhile publication all of its own. And on page 85, in an essay by David Feldman entitled Capitalism, Commerce and Antisemitism I found this: “At the turn of the 20th century, the idea that the British war in South Africa was being fought on behalf of Jews was commonplace among its radical opponents.

"The best known analysis along this line was made by the economist and journalist John Atkinson Hobson. The war, he argued, was being fought under the cloak of patriotism in the interests of financiers among whom ‘the foreign Jew must be taken as the leading type’.”

It occurred to me that I had come across Hobson quite recently in another context and for a moment I couldn’t quite recall where. Then it hit me. It was the book I’d bought a few weeks back. Imperialism by J A Hobson, with a foreword by Jeremy Corbyn.

I’d bought it because I have always regarded anti-imperialist thinking as the key to understanding the Labour leader. But I had other things going on and I had put it to one side when it arrived. Now I picked it up and read it.

Sure enough Hobson’s theory of imperialism was that imperial adventures were conducted by nations on behalf of the finance houses of Europe. They needed constant new markets and then require military might to protect their foreign investments. By owning the press they persuaded European citizens to regard the interventions as patriotic, civilising missions.

And critically, before laying out this theory, Hobson observed that all these finance houses were owned by Jews. A conclusion, his biographer noted that, he didn’t support by research but merely by noting that they mostly seemed to have Jewish sounding surnames.

Mr Corbyn in his foreword, praised the thrust of Hobson’s argument, his theory about finance houses, despite the fact that, if he read it, it would have been obvious that the theory was antisemitic. As it would if he read anything about Hobson, who had been famously and in some detail antisemitic in his writing.

So I knew I had an article to write. I knew it was important politically and impactful journalistically. But I also knew one other thing. If, or rather when, I wrote it, I would have to put up with days of attack on social media from Mr Corbyn’s devoted admirers. And so it proved.

I was only doing it to undermine Labour’s local election campaign, apparently. No. I published when I finished the research and before anyone else had the same idea.

Tony Blair and Gordon Brown had both endorsed Hobson’s book and I was holding Mr Corbyn to a different standard. No, they had both mentioned his very varied life’s work in a single sentence. Neither of them had endorsed Hobson’s theory of imperialism nor would they have done. Indeed a major reason Mr Corbyn wrote a foreword to the book was because he saw it as a sort of rebuke to Tony Blair.

Hobson’s book only mentioned Jews obliquely and in a few sentences. It was unfair to expect Mr Corbyn to mention it. Well, again, no. These few sentences followed an entire Hobson book which went on and on about Jews. And they established that finance houses were dominated by Jews before arguing that imperialism was the fault of finance houses.

This last, particularly absurd, argument was supported by Professor Geoffrey Alderman, a distinguished academic but someone whose desire to be contrarian appears on this occasion to have trumped a reasonable assessment of the evidence.

On and on it went. And something funny happened. The more it went on, and more tiresome it became, the more sure I became that it was worthwhile.

Daniel Finkelstein is Associate Editor of The Times