Ralph Miliband, the father of Ed and David, dissected it well. He was a Marxist who retained the capacity for independent thought, and got into a furious argument with Marcel Liebman, a fellow Marxist Jew, at the time of the Six Day War of 1967. Miliband pointed out an essential truth: that the corrupt regimes of the Middle East needed Israel and anti-Semitic conspiracy theories to distract the attention of their peoples. "If Israel did not exist, they would have to invent it," he said.

 He despaired of the willingness of leftists to go along with Nasserite Egypt. His friend, like so many others, indulged Colonel Nasser even though he had used former Gestapo officers to turn Egypt into a repressive military dictatorship that, despite the Arab Spring, survives to this day. All Nasser had to do was shout about "socialism", "imperialism" and "revolution", said Miliband, and they would come running. "The sad thing is that this sterling Left is incapable of distinguishing anything from anything, and reacts with a truly Pavlovian predictability to the slogans used to make it drool on cue."

Now as then, nothing makes the sterling Left's spittle flow more freely than mention of the state of Israel. They may not know it, for they know very little, but the origins of their Pavlovian response lie deep in the terrible history of the 20th-century Left.