Fears raised 'free NHS' will come to an end
Fears are being raised that the NHS in England will no longer be free at the point of use within 10 years.
Nearly half of the 78 health and care leaders surveyed by the Nuffield Trust felt the status quo would not remain because of the squeeze on funding.
The think tank warned of a "funding crisis this year or next" and that patient care could start to suffer.
The government called this an "unrealistic picture", but Labour said NHS finances were in a "dire state".
Currently the health service gets just over £100bn a year.
The Nuffield Trust said another £2bn a year may be needed to keep pace with demand.
The review of spending since 2010 highlighted the growing number of NHS trusts falling into deficit as a sign of growing problems in the health service.
Provisional figures for 2013-14 show 66 out of 249 trusts finished the year in the red.
The overall deficit was about £100m, compared with a £383m surplus the year before.
Report author Andy McKeon said the difficulties were likely first of all to lead to rising waiting times.
"The NHS has risen to the challenge of living within its means over the past three years," he said.
"But it has now reached a tipping point. The NHS is heading for a funding crisis this year or next."'Unrealistic picture'
The warning comes after similar claims by the Health Select Committee and bodies such as the Royal College of Nursing and Royal College of GPs in the past fortnight.
Rob Webster, chief executive of the NHS Confederation which represents NHS trusts, said: "Staff have worked incredibly hard over the last four years to deliver unprecedented savings while public finances have been constrained, but the challenge is getting much more difficult."
Shadow health secretary Andy Burnham said: "Everywhere you look, there are signs of an NHS now heading rapidly in the wrong direction.
"It is not just standards of patient care that are getting worse but NHS finances are in a dire state."
But Health Minister Lord Howe said: "These predictions are pessimistic and paint an unrealistic picture of how our NHS is working."
He acknowledged unprecedented demands were being placed on some parts of the NHS, but pointed out that the budget had been protected during this Parliament.