A false news story claiming that a Labour activist punched a Tory advisor has spread across social media after being amplified by some of the country's leading political journalists.
But the police have confirmed that there are no reports of any incident taking place, and video appears to show that the supposed punch was actually an advisor walking into a protestor's hand.
The incident happened after health secretary Matthew Hancock was dispatched to Leeds General Infirmary in an attempt to stem the controversy over a picture that showed a sick child who had been forced to sleep on the floor because of a lack of beds.
Mr Hancock's visit came amid growing anger over the Conservative response to the photograph. He was sent after Boris Johnson refused to look at the photograph during an interview, a decision that led to fury on social media and criticism of the Tory party.
Soon after Mr Hancock arrived at the hospital, a flurry of reports suggested that a Labour protestor had attacked one of his aides outside.
The BBC's political editor, Laura Kuenssberg, said that activists had rushed to the hospital and that it "turned nasty when they arrived – one of them punched Hancock's advisor". ITV's political editor Robert Peston suggested that the advisor had been "whacked", and other political reports posted the claims.
None of those tweets gave the name or details of who they had heard about the attack from. While Ms Kuenssberg and ITV's Paul Brand explicitly said the reports had come from the Conservatives, they gave no more information, and others reported the claim as if it was fact.
Those claims were then carried across much of the press, with push notifications and breaking news alerts sent out to readers.
As other news organisations scrambled to verify the original claim, it started to become clear that there had been no such attack. The police said that it had received no reports of any such attack.
"We are aware of information circulating on social media in relation to an alleged incident involving election campaigners at Leeds General Infirmary this afternoon," West Yorkshire Police said in a statement.
"We are currently unaware of any reports to West Yorkshire Police of this nature but are seeking to verify."
Nobody who was involved is understood to have filed a report with the police, and the incident only came to their attention through social media.
Shortly after, video emerged of the incident. It showed that Mr Hancock's aide had not actually been punched – and that instead he had walked into the hand of a man who was not facing him and had been pointing to his side.
Many of those who shared the original claim posted that footage with some indication that their earlier claims were wrong.
Robert Peston, who had shared the original claim, said he had been told about it by "senior Tories". He admitted that there had been no punch.
"It is completely clear from video footage that [Matt Hancock's] adviser was not whacked by a protestor, as I was told by senior Tories, but that he inadvertently walked into a protestor's hand," he wrote. "I apologise for getting this wrong."
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