Two things happened this week - one public and one personal - that didn't seem to be connected. But, when I thought about them for a little while, I realised that they were.

The first was the suspension of Jackie Walker from the Labour Party. And then her reinstatement after an investigation. The suspension was caused by her remarks about Jews financing the slave trade and unless there is a bit of the story missing - she didn't say what she was quoted as saying, for instance -- the reversal seems incomprehensible.

The second, the personal one, was that I found a video of my father that I didn't realise existed, and for the past few days I have been listening to him tell the story of his wartime experiences, and those of his father.

I'll start with that as I think it will make it easier to understand the connection.

My dad tells of his father's arrest and release from a Soviet prison. When, in 1941, Hitler turned his attack on the Soviet Union, Stalin released his Polish prisoners and allowed them to form an army under General Anders, whom he also released from jail. My grandfather was determined to join. But there was a problem.

When he was applying he was asked his ethnicity and, naturally, replied: "Jew". The officer conducting the interview looked up. He asked whether my grandfather really wanted to serve. Assured that he did, under ethnicity the officer wrote: "Pole."

Stalin forbad Anders from recruiting Jewish soldiers. To allow Jews to join a Polish army would be to acknowledge the existence of a Polish multi-ethnic nation. This was something Stalin was attempting to eradicate along with the dangerous nationalism the Soviets maintained that it produced. At every stage, the officers of the Anders army had to employ subterfuge to allow Jews to be part of their force. It was desperately needed later when the army was evacuated to Iran. There was a real danger that Jews would be left behind.

The Soviet ruling was nakedly discriminatory and, even with the help of General Anders, many Jews died as a result of it. They, and their dependents, were not able to link up with the army, which left them without food or shelter.

Yet the Soviets would, I am sure, have resisted the suggestion that they were being antisemitic. Their ruling was to do with Poland and nationalism, not to do with Jews, and if Jews had to suffer the consequences, well that was just bad luck. Indeed, it is one of the many ironies of the Soviet action that one of their attacks on Polish nationalism was precisely that it was antisemitic.

The Soviets even used the bar on Jews from the Anders army as evidence of the dangers of Polish nationhood, even though they had imposed the bar themselves and the Poles had sought to evade it. Many Jews, aware only that it was a Pole who had refused them entry, accepted the Soviet narrative.

Now let's look at Jackie Walker. She drew upon an extraordinary antisemitic slander invented by the militant African American group, the Nation of Islam, one that belongs at the loopy end of anti-Jewish conspiracy theories, along with "why did all the Jews have the day off on 9/11?" Yet watching her on television, she appeared genuinely bewildered to be accused of antisemitism. She doubtless sees herself as the ultimate progressive.

She was, you know, merely speaking up for African Americans, not doing down the Jews. She may have persuaded others in the party of this, leading to the mystifying decision to reinstate her.

These two examples, far apart though they seem, are in the same chain. The left is not antisemitic, it can't be because it is progressive. Being progressive means destroying nationalism, ending capitalism and eradicating imperialism. And if doing that means pushing Jews out of the way, it's not because they've anything against them, you understand. The Jews are just incidental.

Antisemitism on the left appears a mystery. How can people that right on be so right off? It's only understandable if you see how we Jews get in the way of far left conclusions and solutions. The antisemitism isn't on purpose I hope you see. Some of their best friends are Jewish.

Daniel Finkelstein is associate editor of The Times