Sadiq Khan has spoken of his dismay at Nigel Farage’s “desperate” denials of allegations of teenage racism as he described how his experience as a child shaped his life.

The mayor of London said testimony from more than 20 individuals who made allegations about the Reform leader had summoned memories of his own past.

“Being called the ‘P word’ at that age doesn’t just hurt you, it changes you,” he said. “It changes how you pronounce your name. It changes the way you talk to your friends, and it changes the way you walk down the street. These are experiences you never forget. I still remember vividly how I felt.”

Khan said he could not understand why Farage had failed to apologise to the individuals who were contemporaries of his at Dulwich college in south-east London.

Khan, 55, said 61-year-old Farage’s suggestion that the alleged abuse could be dismissed as “banter” that was of its time failed to recognise the impact on those on the end of it. “Growing up in London in the 70s and 80s, I was no stranger to racist abuse,” Khan said. “Those responsible might have thought it was a bit of harmless banter, but I’ll never forget how their words made me feel.”

Khan, the son of a bus driver and a seamstress from Pakistan, has spoken before of facing abuse during his childhood in Tooting, south London.

Khan revealed in 2019 that practically everyone outside his immediate family had been pronouncing his name incorrectly, as “Sad-eek” rather than “Saad-ick”.

Farage has been under growing pressure to apologise for his alleged behaviour at school, including the claims that he targeted abuse of a number of people.

Peter Ettedgui, 61, who is now an Emmy- and Bafta-winning director, told the Guardian that Farage would “sidle up to me and growl: ‘Hitler was right,’ or ‘Gas them,’ sometimes adding a long hiss to simulate the sound of the gas showers.”

His alleged abuse spanned six years, from age 13 to 18.

Khan said: “I’m sure that the multiple reports that Nigel Farage regularly used vile racist and antisemitic language as a London schoolboy will strike a nerve with all those who were on the receiving end of racism growing up. We’ve made huge progress as a society since then, but we risk normalising racism like we did decades ago. Racism has the same long-lasting impact on people now as it did then, and we need to keep calling it out.”

In legal letters ahead of publication of the Guardian’s investigation, Farage’s lawyers claimed that “the suggestion that Mr Farage ever engaged in, condoned, or led racist or antisemitic behaviour is categorically denied”.

Farage later seemingly shifted his position in an interview with the BBC’s political editor in Wales: “Have I said things 50 years ago that you could interpret as being banter in a playground, you could interpret in a modern light today in some sort of way? Yes.”

He added that he had “never directly, really tried to go and hurt anybody”.

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Farage subsequently issued a new statement: “I can tell you categorically that I did not say the things that have been published in the Guardian aged 13, nearly 50 years ago.”

Khan said he believed those who had spoken to the Guardian were right to do so. “While Farage desperately tries to dismiss his actions as the harmless antics of an average teenager, many will disagree, not least his old classmates who remember what happened very clearly.

“They were right to speak out, and Nigel Farage’s refusal to apologise speaks volumes about the character of a man who claims he wants to be the prime minister of this country.”

The government has seized on the claims carried by the Guardian, leading Farage to claim the allegations were politically motivated.

On Thursday, Keir Starmer visited Bushey United Synagogue in Hertsmere. Asked about the claims about Farage and the Reform leader’s response, the prime minister said: “Let me go to the heart of that question. This afternoon in Bushey I’ve spoken to a number of different groups, including Jewish students, young people, children at school. They’ve described to me some of the antisemitism they’ve experienced. It has massively impacted them.

“It is really difficult for them to even talk about it, and I know they’re going to carry that for years and years; this is not just something that can be passed over. Now, these allegations were made in relation to Nigel Farage. They’re serious. They affect human beings in a visceral way.”