A&E figures have hit a record low for the second time in under a year, as hospital chiefs warn the government of a "watershed moment" for the NHS.
On average, trusts managed to see 85.1 per cent of emergency patients within four hours in December - equalling January 2017's all-time low.
The target of 95 per cent has not been met since July 2015.
It comes as the heads of more than 60 emergency departments warned Theresa May that patients are "dying prematurely" in the corridors of A&E units.
And NHS Providers - the trade body which represents NHS services - wrote a letter to Health and Social Care Secretary Jeremy Hunt calling for a £153 billion increase to the NHS budget by 2023.
The body had previously warned the health service was "not where it would want to be" heading into winter amid concerns over a bad strain of flu.
Chief executive Chris Hopson wrote: "There is so much at stake. We can fix this, but there must be no more delay. The ball is now firmly in the Government's court."
His concerns appeared to be backed up when, on Thursday, official figures revealed there had been 48 flu-related deaths so far this winter - with 24 in the last week of 2017 alone.
Figures from NHS England were also released which showed more than 5,000 people were forced to wait more than an hour to be seen in emergency departments in the first week of January.
More than 16,600 people had to wait more than half an hour.
In one bright spot, the numbers of delayed transfers of care - ie when a patient is ready to leave hospital - were lower than at the same point for any of the past four years.
Glen Garrod, vice president of the Association for the Directors of Adult Social Services (Adass), said this was "evidence that putting extra funding into social care, as the Government has done this year, can bear fruit".
Copson asked Hunt for help with the immediate financial impact of "exceptional winter pressures" - exacerbated by the rising numbers of flu cases - arguing that despite planning "more thoroughly" than ever before for winter, "it hasn't been sufficient".
The three-page letter calls for the Government to commit to a long-term increase to the NHS budget - with £153bn being the sum which the Office of Budget Responsibility estimated was needed given projected increased demand for services.
He wrote: "The NHS is no longer able to deliver the constitutional standards to which it is committed. We need to be realistic about what we can provide on the funding available."
"If we continue to run the NHS at close to 100% capacity, day in day out, permanently in the red zone, it's not surprising that the service can't cope when we get a high, but entirely predictable, spike in demand."
A Department of Health and Social Care spokesman said: "The NHS was given top priority in the recent Budget with an extra £2.8bn allocated over the next two years, and was recently ranked as the best and safest healthcare system in the world.
"We know there is a great deal of pressure in A&E departments and that flu rates are going up, and we are grateful to all NHS staff for their incredible work in challenging circumstances.
"That's why we recently announced the largest single increase in doctor training places in the history of the NHS - a 25% expansion."