Doctors will kickstart a debate about patients paying for NHS care by arguing that everyone should receive a set of core services free but charges should be introduced for others.

Delegates at the British Medical Association's annual conference will propose on Monday that ministers contemplate bringing in what would be highly controversial fees for accessing certain health services, as a way of ensuring that the NHS continues to be viable.

Doctors will tell the 500-strong gathering in Edinburgh that they have to "face the unpalatable truth that free at the point of contact can no longer be sustained".

Advocates of charging claim it would help the NHS continue to provide a comprehensive list of agreed basic services and cope with the tight budgets it is expected to receive for years to come and the relentlessly rising demand for treatment caused by an ageing population.

Gordon Matthews, a hospital consultant who is a member of the BMA's consultants committee, is expected to tell the BMA's annual representative meeting: "There has never before been a more important time for the government, the opposition, doctors and other health professionals to engage with the public, to explain the issues and seek consensus as to what priorities are for health and social care, and making explicit what can be funded from central taxation and what cannot. A publicly funded and free-at-the-point-of-delivery NHS cannot afford all available diagnostics and treatments."

Malcolm Grant, the chairman of NHS England, recently suggested that the pressure facing the NHS in the next few years amid continuing tough public spending restrictions meant the next government would have to consider introducing charging, although he also made clear that he did not back such a move.

"It's not my responsibility to introduce new charging systems but it's something which a future government will wish to reflect [on], unless the economy has picked up sufficiently, because we can anticipate demand for NHS services rising by about 4% to 5% per annum," he told the Financial Times in an interview in April. Some countries, including the Republic of Ireland, already charge patients for accessing certain services such as seeing a GP.

The NHS in England is in the third year of a four-year drive to make £20bn in "efficiency savings" by 2015 to release resources to pay for the extra demands placed upon it by the growing numbers of elderly people who need help with dementia or long-term conditions such as heart trouble, breathing problems and diabetes and broken hips, plus big increases in drug costs.

Health economists predict that the NHS is facing more years without real-terms budget increases and will have to make even bigger savings in the future.

Health unions and patient groups voiced disquiet at the prospect of charges. Katherine Murphy, the chief executive of the Patients Association, said the need to improve NHS care after scandals such as Mid Staffs and Morecambe Bay meant it was the wrong time to debate the introduction of fees, which could lead to a two-tier NHS.

"Do you ask people to pay for hospital food? What happens to people who can't pay for it? Who is in a position to say: 'You can't have this operation unless you pay for it yourself'?" she told the Times.

But she accepted that "we do have to have a grown-up conversation with regard to co-payments and top-ups. But with scandal after scandal in the NHS the public wants us to address those now. Unless care is made better, we cut down on waste and the public sees the NHS putting its house in order I don't think it is the time for that conversation," said Murphy, an ex-NHS nurse and manager.

The co-leader of the National Health Action Party Dr Clive Peedell rejected the notion of charges. "The introduction of NHS top-up fees would be irresponsible, dangerous and an administrative nightmare. We do not want to go down that road."