No 10 has no intention of apologising for the PM's false claim that Sir Keir Starmer failed to prosecute Jimmy Savile, after the Labour leader was targeted by protesters near Parliament.
Boris Johnson is facing fresh calls from Tory MPs to say sorry, after protesters were heard shouting about the sex offender, as well as protesting about Covid measures.
But a senior source told the BBC: "He's got other stuff to get on with today."
Mr Johnson did condemn the harassment.
In a tweet, he said the behaviour directed at Sir Keir on Monday afternoon was "absolutely disgraceful" and "completely unacceptable".
But a No 10 source said it was unreasonable to suggest that what happened on Monday "was Boris's fault and not the mob's fault".
At least seven Tory MPs later linked the incident to the PM's incorrect comment and demanded the prime minister said sorry.
However, Northern Ireland Secretary Brandon Lewis said the PM had made a "fair and reasonable point" about Sir Keir taking responsibility for the organisation he led, and nobody should use the remarks to "excuse behaviour from thugs".
Videos on social media showed Sir Keir being escorted into a police car on Victoria Embankment shortly after 17:00 GMT, close to Portcullis House - an office building used by MPs.
Protesters could be heard repeatedly shouting "traitor", while criticising the Labour leader for supporting Covid vaccinations and not "opposing the government" or protecting the working man.
Some protesters were seen holding signs opposing mandatory vaccinations and restrictions to curb the spread of Covid.
But there were also shouts about attacks on journalists, Wikileaks founder Julian Assange, and about protecting paedophiles, naming Savile.
Some MPs have linked these remarks to the false claim that Mr Johnson made in the Commons last week, when he said Sir Keir "spent most of his time prosecuting journalists and failing to prosecute Jimmy Savile".
Scotland Yard later said a man and a woman were arrested after a traffic cone was thrown at officers.
'Misconstrued'
Technology Minister Chris Philip told BBC Breakfast there was "no way you can reasonably make a link" between what the protesters said and the PM's previous remarks.
He said Mr Johnson's comments in the Commons were "capable of being misconstrued", but that he had clarified in the following days that Sir Keir was not personally responsible for the case.
Criticism came from Tory MPs, including Commons defence committee chair Tobias Elwood who tweeted: "Let's stop this drift towards a Trumpian style of politics from becoming the norm."
And Labour MP Kim Leadbeater, who now holds the seat of her sister Jo Cox, who was killed while serving as a politician, said: "These things don't just happen. Words have consequences, leaders have a duty to behave responsibly and politics is not a game."
Julian Smith, a former Northern Ireland secretary under Mr Johnson, said it was important for democracy, as well as Sir Keir's security, that "the false Savile slurs made against him are withdrawn in full".
Senior Tory MP Sir Roger Gale - who has already called for the PM to resign over the Downing Street party row - also said he feared the "grim scenes" outside Parliament were "the direct result of the deliberately careless use of language in the Chamber".