And what has the world learned of all this?” is the handwritten question by Holocaust survivor Henri Obstfeld, which appears beside his image in a 2017 book Survivor. Introducing his portraits of 103 survivors, the photographer Harry Borden writes: “I grew up on a farm in Devon, England. My dad, Charlie, was a resolutely atheist Jew who derived nothing from his background except a fear of antisemitism. When I was a boy he once told me that the Nazis would have killed us. I was shocked. I attended a Church of England primary school, sang in the choir and had always considered myself a Christian like my mum.”

Disquieting also was the size of some responses to the assertion that 'the scale of the Holocaust is exaggerated'

The need to learn from the Holocaust, that hideous marker of where antisemitism leads, was underlined again recently when the Guardian and Observer reported two separate sets of data: the Community Security Trust’s finding that antisemitic incidents in the UK are at a record high for the third successive year; and the results of a poll which found that, as the online headline put it, “One in 20 Britons does not believe Holocaust took place”.

A representative of the Holocaust Memorial Day Trust, which commissioned the poll of 2,006 UK adults, emphasised that the result did not mean poll respondents were active Holocaust deniers, “people who deliberately propagate and disseminate vile distortions. But their ignorance means they are susceptible to myths and distortions.”

Readers responded with a mix of disquiet and indignation. Wasn’t there an important difference, some asked, between not knowing and not believing? Had the article conflated those two categories of respondents, so that the shocking figure of 5.4% disbelievers was misleading?

The article was accurate, as we will see. But the readers’ queries were understandable. There is a material and moral distinction between not knowing about this episode in history, this fact, and being aware of the Holocaust but deciding not to believe the fact. Ignorance of this matter should shame an adult but is reparable. Wilful disbelief, especially if it involves active denialism, is contemptible.

The numbers behind the poll headline are public. (Click the “results part two” button.) To the proposition “the Holocaust never really happened”, responses were: strongly agree 2.6% (53 people, of whom 35 were aged under 45); agree 2.8% (57, 46 under-45s); neither agree nor disagree 6.9% (139, 105); disagree 10.7% (214, 123); strongly disagree 72.9% (1,462, 604); I don’t know 2.8% (57, 36). Twenty-four people (23 under 45) affirmed: “I have never heard of the Holocaust.” Yes, it is a relatively small sample. Strong majorities backed key points, such as the need for more education. And there was caution: only 25% strongly agreed or agreed that “something like the Holocaust couldn’t happen again”, though 21% neither agreed nor disagreed with that proposition.

Disquieting also was the degree of agreement with the assertion that “the scale of the Holocaust is exaggerated”: 8.2% strongly agreed or agreed. To the proposition that “the Holocaust is irrelevant now”, 8.4% strongly agreed or agreed. Another 12.6% responded that they neither agreed nor disagreed with that statement.

Indifference can be a special kind of ignorance.

Frederick Terna, also portrayed by Borden, wrote in his handwritten note: “the aim is a full life in a fair and open community. We are all responsible for each other.”