Survivors of the Holocaust in the UK and a second world war veteran have warned that the lessons of the atrocities that took place are being forgotten, as they marked the 75th anniversary of the liberation of Auschwitz concentration and extermination camp.

The national commemorative event in Westminster on Holocaust Memorial Day (HMD) was attended by more than a dozen Holocaust and genocide survivors, as well as Boris Johnson, the Duke and Duchess of Cambridge, and high profile political and religious figures. It was one of 10,000 events taking place to mark the day around the UK.

Lily Ebert, who was in her early teens when she was sent to Auschwitz, renewed calls for future generations to remember the past. “A few people are very interested about the Holocaust, but not enough. Even today, quite lot of people don’t know about … We [survivors], only a few are still alive and they are already so many deniers,” she said.

“The legacy is very important. Why am I telling my story? People should know that something like that should never happen again. That humans can and are willing to do that to other human beings.”

Arek Hersh, a survivor who lost 81 members of his family and has an MBE for voluntary services to Holocaust education, said: “Certain people have already forgotten quite a few years ago. But, still I go round to schools, universities and so on … I just do the job. To me it’s very important we remember, I lost my whole family and I’m the only one that came to England.”

The Duchess of Cambridge speaks to Holocaust and genocide survivors after the memorial in Westminster. Photograph: Chris Jackson/Getty Images

Born in Poland, Hersh was deported by the Nazis to a concentration camp at the age of 11, then moved to a number of others before being taken to Auschwitz. He was liberated at Theresienstadt in May 1945 and was one of the Windermere children – 300 survivors who were brought to the Lake District after the Holocaust.

Ian Forsyth, a second world war veteran who was among the first troops to liberate Bergen-Belsen in April 1945, said he feared that the lessons from the Holocaust were not being remembered: “I spend my life going round schools talking to whoever cares to listen, but unfortunately it’s difficult for someone who has not been there, who has not seen any concentration camp. It’s very difficult for people who live miles away to understand what’s going and it’s our job to make sure they do.”

Forsyth said he couldn’t believe it’s been 75 years since the liberation of the camps: “It feels like yesterday. The dreams are yesterday, they still haunt me. It took me very much by surprise and it changed my whole life because I could not have believed that human beings could be like that.”

The event also commemorated the 25th anniversary of the genocide in Srebrenica, where about 8,000 Muslim men and boys over the age of 12 were murdered. Survivors of genocides in Cambodia, Rwanda, Bosnia and Darfur were present.

Speaking at the ceremony at Central Hall in Westminster, Johnson said: “As prime minister, I promise that we will preserve this truth forever. I will make sure we will build a national Holocaust and memorial centre so that future generations can never doubt what happened.”

Joe Twilley, head of communications at the Holocaust Memorial Day Trust, said the theme of this year’s commemorative event is to stand together. “We’re thinking about times in history when individuals have taken action to stand together with those who are facing persecution or prejudice or genocide.”

Ebert described her childhood as “very protected”, but said it quickly unravelled once the Nazis invaded Hungary in the spring of 1944. Her family were stripped of their valuables and forced to wear gold stars. They were moved to a ghetto where several families at a time were placed in one room and then moved again, to another ghetto, before being forced on to a train headed for Auschwitz.

Auschwitz-Birkenau was the largest of all the Nazi camps, where approximately 1.1 million people were murdered.

“It was a hot July day in 1944. In one cabin, they put about 70, 80 people; man, woman, children, babies. They put in two buckets, one with water and one for human waste. It was so crammed. You cannot describe this. The smell, the heat, the sound of babies crying. You cannot describe what it really was,” Ebert said.

Ebert said there was at least one thing she wanted people to learn from her: “We have to be tolerant to each other. If somebody is different from us, it doesn’t mean we’re better or worse. It makes no difference what our skin colour, nationality or religion is. One thing we need to remember is that with all human beings, our blood is red. When you cut us, it hurts.”