Nigel Farage must explain reports of racist comments allegedly made by the Reform UK leader when he was a schoolboy, the prime minster has said.

Farage made anti-semitic jibes at a fellow pupil at Dulwich College and taught younger pupils racist songs, according to The Guardian.

The Reform leader denies making any of the comments and actions attributed to him by former pupils at the South London school in the 1970s.

Sir Keir Starmer called on Farage for an “explanation of the stories”, at Prime Minister’s Questions.

Speaking afterwards, the PM’s press secretary said: “These are disturbing allegations and it is vital that Nigel Farage urgently explains himself.”

Among the allegations in the Guardian are that Farage joked about gas chambers and put another pupil in detention, when he was a prefect, for the colour of their skin.

Farage’s former classmate Peter Ettedgui, 61, told the newspaper: “My grandparents had escaped from Nazi Germany, and had always talked with deep gratitude about how they felt welcome in the UK.

“I’d never experienced antisemitism growing up, so the first time that this vicious verbal abuse came out of Farage’s mouth was deeply shocking.”

Another former pupil, who is not named, told The Guardian Farage had taught younger members of the Combined Cadet Force at Dulwich racist football terrace song “Gas Em All”.

In a statement, Reform UK said: “These allegations are entirely without foundation.

“The Guardian has produced no contemporaneous record or corroborating evidence to support these disputed recollections from nearly 50 years ago.”

Speaking to reporters after PMQs, a Reform spokesman said Farage denied making the comments that have been attributed to him.

He added that the Reform leader had no plans to sue The Guardian for defamation “at this stage”.

Asked if Farage would condemn the sort of language being attributed to him if he heard it now, his spokesman said: “Yes.”

And he said that if past comments of this nature came to light when someone was seeking to be a Reform candidate they would be ruled out.

But he added that there would have to be “primary evidence” that they had said it.

Conservative leader Kemi Badenoch’s spokesman said the “issue was for Nigel and the Guardian”.

“This is something that happened something like 40 years ago and it is for the leader of Reform to explain, not the leader of the Conservative Party.”