Keir Starmer has accused the prime minister of "dragging everybody into the gutter" following his bizarre rant about Jimmy Savile in the House of Commons.
Boris Johnson came under fire from the Labour leader after Sue Gray delivered her initial findings on parties at No 10 Downing Street.
In response, Mr Johnson falsely claimed Sir Keir had failed to prosecute notorious Leeds paedophile Jimmy Savile while in charge of the Crown Prosecution Service (CPS).
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As reported by the Mirror, the prime minister was advised by his own MPs against making such claims, but he ignored the advice and said: "He spent most of his time prosecuting journalists and failing to prosecute Jimmy Savile, as far as I can make out."
Sir Keir led the CPS in 2009, when Savile escaped prosecution due to insufficient evidence. It has since come to light that Savile sexually abused hundreds of children and women during his career.
The CPS has since apologised for failing to prosecute Savile, but an investigation from the Full Fact website revealed the Labour leader was never personally involved in the decision.
A CPS spokesperson told Full Fact: ""There is no reference within the [investigation] report to any involvement from the director of public prosecutions [Sir Keir's role from 2008 until 2013] in the decision-making in the case.
"The reviewing lawyer at the time set out their own reasons for the decisions they took."
One Tory MP has said the prime minister's outburst was "totally outrageous" and Sir Keir has responded today in a passionate interview with Good Morning Britain.
He said: "It’s a slur, it’s untrue, it’s desperate from the Prime Minister.
“I was really struck yesterday in the House at how many Conservative MPs were disgusted at that untruth from the despatch box.
“Of course on our side, people were disgusted. But his own MPs couldn’t believe their Prime Minister had stooped that low.
“He’s degraded the whole office. And this is how he operates. He drags everybody into the gutter with him.
“Everybody he touches, everybody that comes into contact with him is contaminated by this prime minister.”
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Even Dominic Raab, one of the PM's key allies, was unable to defend his actions.
When quizzed on why Mr Johnson had brought up the Savile reference, Mr Raab said: "I can’t substantiate that."
He later tried to claim it was simply "the cut and thrust of parliamentary debates and exchanges".
The ill-judged remark from the PM came as he was responding to the initial findings from Sue Gray's long-anticipated report into Tory parties during the height of the coronavirus lockdown.
A brief version of the full report was released, so as not to jeopardise an ongoing Met Police investigation, but senior civil servant Ms Gray didn't hold back in her scathing assessment of the culture at No 10.
She said the behaviour of those at the parties was "difficult to justify" and added: "At least some of the gatherings in question represent a serious failure to observe not just the high standards expected of those working at the heart of government but also of the standards expected of the entire British population at the time."
She added there was "too little thought given to what was happening across the country" and said there were "failures of leadership".
Speaking to Good Morning Britain, Mr Raab was asked whether the PM should resign over the findings.
"Let’s wait and see," he said.
"Allow the police to conduct their investigation and see, when they have ascertained the facts, quite what they conclude.
"Of course, there will be full transparency around that."
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