A study by mutual Benenden Healthcare Society found only 41% of those questioned believe the NHS will be there for them in 10 years' time.
There is a further drop to one in three (33%) when looking ahead to 20 years' time. Significantly, half of those questioned also believe that present Government's policies will weaken the NHS over the next couple of years.
Only 11% believe the recent government reforms will strengthen the positioning of the NHS in the future.
The findings of the survey demonstrate public concerns about the amount of health spending that is invested in private profit-making healthcare providers - highlighting the public's preference to see more money being invested in the NHS.
Those polled would also rather see more of a balance between the provision of health services by the private profit-making sector and the not-for-profit sector (i.e. healthcare organisations based on a mutual funding model which use contributions from members to fund healthcare services).
Respondents believe that only 13% of healthcare spending should be spent on private healthcare, but that in 10 years' time think this would likely increase to 30%.
The research results show that whilst 89% of people believe that the NHS would be there to provide good quality healthcare in the case of an acute emergency (e.g. a road accident or a heart attack), public confidence falls for longer-term chronic conditions, including those associated with an ageing society.
Only 48% of those polled believed that the NHS would provide good quality healthcare services in the case of a chronic condition such as a stress or back pain.
Ken Hesketh, Chief Executive of Benenden Healthcare Society, said: "What these findings ultimately show is that there is a real need for further consideration and debate around the future of healthcare provision and how improvements in standards can be financed going forward."
And whilst the results show that a majority of the public would still want to see their GP for free, nearly one in five (17%) are willing to spend small amounts (£5 a month) extra for seeing their hospital consultant more quickly with a further 13% willing to pay more than £5 a month.
Similarly 27% would pay extra to receive inpatient care and 22% to access free physiotherapy.
Ken Hesketh continued: "Realistically, the country's public finances are unable to sustain a level of health spend that the public have come to expect in the past decade and the role of ‘top-up' payments and co-payment plans will be crucial for the continuation of good quality healthcare.
This means that there is a real place for mutual organisations such as Benenden Healthcare Society to complement the healthcare provision of the NHS in the future."
