- Johnson repeated a false claim that Keir Starmer failed to prosecute the sex offender Jimmy Savile.
- Experts compared it to Pizzagate and warned it could embolden QAnon in the UK.
- Conservative MPs have called for him to withdraw it, and plan to submit letters of no confidence.
Boris Johnson's use of a far-right conspiracy theory against political opponent Sir Keir Starmer is "Trumpian" and could embolden groups like QAnon within the UK, experts told Insider.
The prime minister on Monday claimed that Labour's leader, the former chief prosecutor in the UK "spent most of his time prosecuting journalists and failing to prosecute Jimmy Savile, as far as I can make out."
Savile, a longtime BBC presenter, was a serial sex offender who died before any action was taken against him.
Johnson's decision to invoke this claim – which has circulated among far-right fringe groups online but been widely debunked – has caused widespread consternation among his own backbenchers.
It has also prompted at least one member of his Government to consider their role, with the MP telling Insider they did not want to be associated with such allegations.
Experts also warned that it could result in the UK's democratic dialogue backsliding further.
Will Moy, chief executive of fact-checking organisation Full Fact, told Insider: "A prime minister's words matter and they can be absolute rocket fuel for conspiracy theories. They can be taken at face value, they can be twisted but whatever they do, they have consequences."
He added it was "not so different to Pizzagate", the debunked conspiracy theory claiming Hilary Clinton was involved in a child sex ring, which went viral in the US in 2016.
"One consequence of him doing this is that the profile of this claim will just get bigger online," said Moy.
That view was shared by Chris Curtis, a political pollster for Opinium.
While noting that "beyond a small minority" of conspiracy theorists it was unlikely to change minds about Starmer, the use of the smear was still "problematic".
"There will be some people who exist within the QAnon universe who feel the Prime Minister has lent legitimacy to their position," he tweeted. "That could have pretty negative consequences."
Several within the Conservative party have also gone public with their concerns about it, and many MPs have called for Johnson to apologise and withdraw his comments.
Julian Smith, a former chief whip and Northern Ireland Secretary, said: "False and baseless personal slurs are dangerous, corrode trust and can't just be accepted as part of the cut & thrust of parliamentary debate."
Bob Neill, a fellow Conservative MP, agreed, saying: "This suggestion is baseless and unworthy, even in the cut and thrust of political debate."
Rory Stewart, a former minister who ran against Johnson in the 2019 leadership contest, said: "The sheer tawdry Trumpian shabbiness of the whole thing — it is difficult to see how much more of this the party or our political system can survive."
On Wednesday morning Tobias Ellwood, chairman of the defence committee, said he would be submitting a letter of no confidence and cited the Savile comments as one of the factors.
Speaking on Sky News, Mr Ellwood said: "Attacking this week Keir Starmer with Jimmy Savile… I mean who advised the Prime Minister to say this? We're better than this, we must seek to improve our standards and rise above where we are today."
He added: "I don't think the Prime Minister realises how worried colleagues are in every corner of the party, backbenchers and ministers alike, that this is all only going one way and will invariably slide towards a very ugly place."