Labour has accused Boris Johnson’s campaign of “lying and cheating” to try to distract attention from the prime minister’s insensitive reaction to a sick four-year-old boy forced to sleep on a hospital floor.

With just days to go until polling day, the Tories suffered one of their worst days of the campaign as Johnson refused on camera to look at a picture of the poorly child and pocketed the phone of the reporter who tried to show it to him.

The incident escalated when Matt Hancock, the health secretary, was dispatched to Leeds General Infirmary in an effort to show that the party was taking the case seriously. But Johnson’s team ended up trying to deflect the story on to Labour by wrongly briefing that a Tory aide was “punched” outside the hospital by a leftwing activist.

The claims quickly turned out to be untrue when video footage showed that the adviser was accidentally brushed in the face.

“The Tories are so desperate to distract from a four-year-old boy sleeping on a hospital floor because of their cuts to the NHS that, once again, they have resorted to barefaced lying,” a Labour spokesperson said. “This is a new low and the Conservative party has serious questions to answer.”

John McDonnell, the shadow chancellor, tweeted: “Johnson and the Tories lie and they cheat to manipulate the media. A sick child treated on the floor of a hospital and they try divert attention with a dead-cat lie story. Never has our politics sunk so low in our country.”

The Tories struggled to get to grips with the story of the sick child after the Daily Mirror printed the picture of him on their front page. In an ITV interview during a campaign visit, the prime minister was challenged about the image of Jack Williment-Barr sleeping under coats on a hospital floor in Leeds as he waited for a bed, despite having suspected pneumonia.

Asked if he had seen the photographs, Johnson said he had not. The ITV reporter, Joe Pike, then showed the prime minister the photograph on his phone, describing what it portrayed.

Johnson declined to look, saying: “I understand. And obviously, we have every possible sympathy for everybody who has a bad experience in the NHS.” He went on to discuss investment in the NHS and Brexit.

Pike pressed the point: “I’m talking about this boy, prime minister. How do you feel, looking at that photo?” Johnson replied: “Of course. And let me tell you … I haven’t had a chance to look at it.” Pike asked: “Why don’t you look at it now, prime minister?” Johnson, still not looking at the photo, replied: “I’ll study it later.”

Pressed again, he said: “If you don’t mind, I’ll give you an interview now. What we are doing is we are taking this country forward, and we are investing in the NHS.” Johnson then appeared, out of camera shot, to take the phone out of Pike’s hand and put it in his coat pocket.

The reporter challenged him: “You’ve refused to look at the photo, you’ve taken my phone and put it in your pocket, prime minister. His mother says the NHS is in crisis. What’s your response to that?”

At this point, Johnson removed the phone and looked at the picture for the first time: “It’s a terrible, terrible photo, and I apologise, obviously, to the family and all of those who have terrible experiences in the NHS. But what we are doing is supporting the NHS and, on the whole, I think patients in the NHS have a much, much better experience than this poor kid has had.”

Johnson ended by handing back the phone: “I’m sorry to have taken your phone. There you go.”

Jeremy Corbyn responded by tweeting a video of the exchange with the message: “He just doesn’t care.”

The Labour leader later added: “He took the phone off Joe. Strange behaviour. I don’t think anyone should behave like that. Whilst sometimes lots of questions from journalists do irritate politicians, that’s the way it is, it’s part of the democratic process. I don’t think that’s the kind of behaviour we should be doing – I would never do that.”

At a subsequent media Q&A at the warehouse, Johnson was twice asked about his reaction in the interview, but declined to address the questions, instead talking about investment in the NHS.

Asked later by the Guardian why he had not acknowledged the photo, he said: “I did. I did. I did. Next question.”

Johnson has previously been accused of showing a lack of empathy, for example during a speech at a police training college in September, when he pressed on with a speech even after a cadet directly behind him half-collapsed.

The incident was compounded by the Tories’ apparent attempt to distract from Johnson’s behaviour by wrongly accusing a Labour activist of violence. The party was forced to make an embarrassing climbdown after aides initially briefed that an adviser to Hancock been hit by one of a group of Labour protesters in an incident that it later emerged had been innocuous.

Having later been shown footage of the alleged incident, aides were forced to acknowledge that it looked as if the adviser was hit in the face accidentally, but still tried to turn the story against Labour by claiming that the activists’ behaviour and language had been unacceptable.

West Yorkshire police later said they were “unaware of any reports” of an incident involving election campaigners at the hospital. Hancock and his aide were both heckled, with people shouting, “Shame on you”, “We do not want you in this country” and “You are not welcome in this hospital” as they both walked to a waiting car, but a source present at the scene said they had seen no sign of the incident described by Tory aides.

The aide to the health secretary has not responded to a request for comment.

The chaotic day for the Tory campaign came after Johnson criss-crossed target seats in north-east and south-west England by chartered plane. The prime minister acknowledged criticism over the environmental cost of taking a short 25 minute flight between Doncaster and Teesside, but insisted the carbon emissions had been “offset”.

On Tuesday, Johnson is due in Staffordshire, where he will rail against the threat of tactical voting to his chances of getting a majority.

The pressure remained on the Tories on Monday evening as further reports emerged of long wait-times in NHS facilities. Birmingham Children’s hospital confirmed one young patient had been left for 17 hours in A&E on Saturday, saying it had been “exceptionally busy over the last two weeks”. Giving context, a spokesman said the average waiting time that day was about four and a half hours.

Tuesday’s Daily Mirror ran another story about a sick child the paper said had been made to wait for hours before being seen. The Mirror reported that nine-month-old Lily Webb had spent six hours on a chair in A&E with just her mother’s cardigan as a blanket. The front page story bore the headline: “Here’s another picture you won’t want to look at, Mr Johnson.”

The Independent said it had seen a leaked NHS email that said a 12-year-old with learning disabilities and mental health issues had spent 57 hours in an Essex hospital’s A&E department waiting for a specialist bed to become available. The trust declined to comment on Monday evening.

Speaking on the campaign trail earlier on Monday, Corbyn said the Tories’ response to the case of the sick child had been unacceptable. He said: “They’ve had nine years in office, and whilst they now claim they are funding the NHS, they are not; they’re not even beginning to make up the shortfall it’s had over the past nine years.

“We are determined that we’ll put £26bn in, which will over time amount to £40bn into the NHS, to ensure it’s properly funded – but also social care and mental health services.”