There is no antisemitism in the Labour Party. Don’t take my word for it: Ken Livingstone and Ken Loach have both assured us of this, so we can stop worrying.

You might spot the sarcasm. Ken Livingstone has spent much of his political career baiting Jews and then laughing it off. Telling two foreign-born Jewish property developers to “go back” to their own country. Comparing a Jewish reporter to a “concentration camp guard”. And most recently and heinously, claiming that Hitler “was supporting Zionism” in the 1930s and that there was “real collaboration” between Nazism and the Jewish national movement.

Loach first attached himself to this Stalinist lie that Zionism and Nazism collaborated in the murder of European Jewry three decades ago, when he directed a play called Perdition, written by a Trotskyist playwright called Jim Allen, that dramatized the Kastner trial that took place in Israel in the 1950s.

Rezső Kasztner was a Zionist leader in Hungary who negotiated with the SS while they were organising the deportation of hundreds of thousands of Hungarian Jews to Auschwitz. His supporters point to the 1,300 Jews he managed to save; his detractors, such as Paul Bogdanor’s recent book Kastner’s Crime, claim that in so doing he knowingly assisted the SS in their work.

This tragic and controversial episode is used by Loach, Livingstone and others to try to claim that the entire Zionist movement collaborated in the murder of their fellow Jews; either from cold, cynical calculation – they only cared about getting Jews to Mandate Palestine – or through ideological affinity.

This broader claim is nonsense, of course. Zionists in Hungary saved tens of thousands of Jews and were also betrayed by Kasztner. Hitler believed in a global Jewish conspiracy and feared that the creation of a Jewish state would only strengthen his greatest foe. The idea that Zionism and Nazism have anything in common is grotesque.

So why, out of all the stories of suffering, heroism, cruelty, fear, destruction and salvation that make up the fate of European Jewry under the Nazis, do Livingstone and Loach choose to become experts in the one aspect that makes Jews look bad?

Why, instead of helping to educate the world about the six million Jews who died, do they encourage people to learn about about one Jewish collaborator?

The answer is obvious. Their hatred of Zionism and Israel is so overwhelming, it would even lead them to the softer end of Holocaust Denial. Possibly there is also something deeper, most visceral, to it: Loach has previously spoken resentfully about “the generalised sense of guilt that everyone has about the Jews.”

Perhaps they don’t care that the more they push guilt for the Holocaust onto “the Jews”, the less heavily that guilt weighs on the Nazis. Loach and Livingstone both like to think of themselves as anti-fascists but in this respect they are doing neo-Nazis’ work for them.

The danger is that, by raising doubt about this one aspect of the Holocaust, they cast doubt on all of it. Without directly questioning the core facts of the genocide of European Jewry, they open the door for others, in this conspiracist age, to do precisely that.

So when Israeli-American author Miko Peled said at a fringe meeting that free speech includes discussing “the Holocaust: yes or no” – implying that Holocaust deniers have their place in public debate – Loach refused to condemn Peled’s comment, simply telling the BBC: “history is there for us all to discuss.”

Outside the conference building, a group called Labour Party Marxists was handing out a leaflet titled “anti-Zionism does not equal anti-Semitism” that quoted Reinhard Heydrich, one of the architects of the final solution, claiming that Nazism did not mean any harm to the Jews.

And what used to be far left is now, through the Corbynite revolution, setting the tone and the mood of the Labour Party.Marxists quoting Nazis to slander Zionists – that pretty much sums up the left nowadays.

Dave Rich is the author of The Left's Jewish Problem: Jeremy Corbyn, Israel and Anti‑Semitism