Five percent of UK adults don't believe the Holocaust happened, according to new research from the Holocaust Memorial Day Trust.
A further 8 percent of adults believe the scale of the Holocaust, during which approximately 6 million Jewish people were murdered by the Nazis, was overstated.
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More than half said they didn't know how many Jewish people were killed or grossly underestimated the number. Forty-five percent didn't know the death toll, and 19 percent believe it was fewer than 2 million.
Holocaust Memorial Day Trust chief executive Olivia Marks-Woldman said the level of denial was shocking.
"Without a basic understanding of this recent history, we are in danger of failing to learn where a lack of respect for difference and hostility to others can ultimately lead.
"With a rise in reported hate crime in the UK and on-going international conflicts with a risk of genocide, our world can feel fragile and vulnerable. We cannot be complacent."
Holocaust survivor Steven Frank, one of 93 children who survived the Theresienstadt camp, said the figures were worrying.
"In my experience, people don't have a solid understanding of what happened during the Holocaust and that's one of the reasons I am so committed to sharing what happened to me.
"The only way to fight this kind of denial and anti-Semitism is with the truth. I tell people what happened, what I saw and what I experienced. Education is so important. If we ignore the past, I fear history will repeat itself."
Despite the figures, 83 percent of respondents said it's important to know about the holocaust, and 76 percent believe more needs to be done to educate people on what happened.
The figures came out of a survey of more than 2000 people, weighted to be a representative sample of UK adults.