Video report by Harry Horton
The sister of murdered MP Jo Cox has accused Boris Johnson of "adding fuel to the fire" of public anger directed at politicians by using a false slur against Sir Keir Starmer.
Kim Leadbeater, who succeeded Ms Cox as the Labour MP for Batley and Spen, said she was "knocked for six" by footage of a mob hurling abuse at the Labour leader outside parliament on Monday.
The incident came days after the Prime Minister repeated the widely discredited claim that Sir Keir had failed to prosecute the prolific paedophile Jimmy Savile while he was head of the Crown Prosecution Service.
Mr Johnson has so far refused to apologise for his comments despite pressure from some of his own MPs.
Ms Leadbeater said: "Sadly at the moment we have a Prime Minister who is so focused on saving his own skin everything else is going by the wayside.
"Things don't happen in a vacuum – we know that people are protesting about various things at the moment but when we have a Prime Minister adding fuel to the fire that's not helpful."
Ms Cox was murdered by a far-right extremist in 2016 in a case that caused widespread outrage.
Ms Leadbeater added: "I want to get on with this job, I don't want to have to keep on having to talk about safety and civility in public life but it's only going to change if politicians lead on that."
Among the MPs on Mr Johnson's own side to have criticised his remarks is the Skipton and Ripon MP Julian Smith, who called on the Prime Minister to withdraw the comments.
Brendan Clarke-Smith, the MP for Bassetlaw, said Mr Johnson could have phrased his comments differently.
He said: "He didn't mean it as a personal attack, a personal smear in that sense. I do think he could probably have clarified that at the time."