Sadiq Khan warned against complacency over antisemitism as the capital’s mayor and London Assembly members hosted the City Hall HMD commemoration.

Some guests were moved to tears by an address by Manfred Goldberg, a German-born survivor, who recounted a childhood spent in concentration camps.

Mr Goldberg spoke of the pain of losing his infant brother shortly after they were transported to the Riga ghetto in Latvia — and about working as a slave labourer in a series of camps.

He survived a “death march” after the Stutthof camp was abandoned before being liberated in May 1945.

The 87-year-old said afterwards that he feared the growth of social media, combined with the volatile nature of world politics, would have tragic consequences.

Kemal Pervanic, a Muslim who survived the Omarska concentration camp during the Bosnian conflict, used the theme of this year’s HMD, the power of words, to discuss how propaganda could “sow the seeds of evil”.

Mr Khan told the JC that the lessons from testimonies such as Mr Goldberg’s were “as relevant in 2018 as they were in the 1930s”. There was a sense of urgency about collating the stories of survivors who were still alive.

“You can’t beat witness testimony. It’s powerful. The concern I’ve always had is that as years go on, there are fewer survivors of the Holocaust. We should cherish the memories they have.

“Unless we remember these stories we become complacent — and we can’t do that. We’ve always got to be vigilant against words used in a bad way.”

Joseph Dweck, senior rabbi of the S&P Sephardi Community, used his address to illustrate the “good and bad ways words can be used”, contrasting excerpts from speeches by Adolf Hitler and Sir Winston Churchill.

“The Torah teaches us that it was with the words that God spoke that created the world,” he said. “But words also launched the world war that murdered millions of people.”

The ceremony was attended by representatives of all 32 of the city’s boroughs.