Boris Johnson’s main political rival accused the British Prime Minister on Tuesday of “dragging everybody into the gutter” for repeating in parliament a false claim that he had failed to prosecute one of Britain’s most notorious sex offenders.

During angry and tense exchanges on Monday, Johnson accused Labour leader Keir Starmer “of prosecuting journalists and failing to prosecute Jimmy Savile” during his time as Director of Public Prosecutions, a role for which he later received a knighthood from Queen Elizabeth.

Savile, a celebrated TV and radio host who was never prosecuted despite a number of police investigations and warnings about his conduct, died in 2011, aged 84. After his death it was revealed he had abused hundreds of victims, the youngest of whom was just eight.

Starmer headed the Crown Prosecution Service at the time Savile was being investigated, but the CPS said Starmer was not the reviewing lawyer for the case and he had had no direct role in the decision not to prosecute Savile. Starmer later issued an apology for CPS failings in the case.

“It is a ridiculous slur peddled by right-wing trolls,” Starmer told Sky News, accusing Johnson of debasing his office.

“He’d been advised not to do it (make the false Savile claim), because it is obviously not true. He does what he always does, which is to try to drag everybody into the gutter with him.”

Johnson’s remarks came during a parliamentary session in which he was defending his own integrity after a report found that alcohol-fuelled events had taken place at his office and residence during COVID-19 lockdowns, leading to calls for his resignation from Starmer and some in his own party.

Asked about the exchanges in media interviews on Tuesday, Deputy Prime Minister Dominic Raab declined to repeat the allegation against Starmer, but said the remarks were part of the “cut and thrust” of parliamentary debate.

“I think Keir Starmer should be subject to scrutiny across the board including the calls he’s taken during this pandemic,” Raab told BBC radio. “He should be judged on the calls or frankly, his inability to make those judgement calls, in relation to his own behaviour.”

Starmer said that some Conservative lawmakers had privately shared their concerns with him about Johnson’s remark. Julian Smith, who served as Northern Ireland minister under Johnson, said it should be withdrawn.

“The smear made against Keir Starmer relating to Jimmy Saville (sic) yesterday is wrong & cannot be defended,” Smith said on Twitter. “False and baseless personal slurs are dangerous, corrode trust & can’t just be accepted as part of the cut & thrust of parliamentary debate.”