Boris Johnson has been embarrassed for a second time within days while on a hospital visit.
He was confronted by the dad of a young girl, who is being treated on childrens' ward at the Whipps Cross University Hospital in Leytonstone.
The dad told the Prime Minister there were not enough doctors and nurses.
In a conversation lasting around two minutes, the man said the situation was "not acceptable".
The parent said the situation was "not acceptable" and told the Prime Minister: "There are not enough people on this ward, there are not enough doctors, there's not enough nurses, it's not well organised enough.
"The NHS has been destroyed ... and now you come here for a press opportunity."
Mr Johnson said "there's no press here" but the parent gestured to cameras filming the confrontation, and said: "What do you mean there's no press here, who are these people?"
The Prime Minister responded that he was there to "find out" about problems.
The parent responded: "It's a bit late isn't it? Years and years and years of the NHS being destroyed."
A spokesman for the Prime Minister said the man was understandably "very distressed" and the Prime Minister was "not going to hide away from those circumstances when he goes on these visits, and so obviously is keen to talk to people and empathise and see what he can do to help".
"It's also a reminder of why exactly he is so keen to make the NHS a priority and make sure it's getting the funding that it requires," the spokesman added.
Downing Street said the Prime Minister had spent the past six weeks visiting hospitals "to hear directly from NHS staff and patients - and this is exactly why he is so committed to making sure investment reaches frontline services, so that doctors and nurses have the resources they need and patients receive consistently world-leading care".
A spokesman added: "This is why we've recently invested an additional £1.8 billion into frontline services and are upgrading 20 hospitals across the country."
