Everyone in the UK should start paying a £10-a-month NHS "membership charge" to save it from sliding into a decline that threatens its existence, a former Labour health minister has urged.

Lord Warner, who served under Tony Blair, warns that the NHS will become unsustainable without new sources of funding and painful changes.

"Many politicians and clinicians are scared to tell people that our much-beloved 65-year-old NHS no longer meets the country's needs," Warner writes in the Guardian.

"Frankly, it is often poor value for money. The NHS now represents the greatest public spending challenge after the general election. MPs taking to the streets to preserve clinically unsustainable hospital services only damage their constituents."

Warner, in a report he has co-authored for the thinktank Reform, says dramatic action is needed as the NHS faces an expected £30bn-a-year gap by 2020 between the demand for healthcare and its ability to respond, and needs several new funding streams to remain viable.

Revenue could also come from higher, hypothecated "sin" taxes on alcohol, tobacco and gambling, and taxes on sugary foods because of rising obesity.

Inheritance tax needs to be collected from more than the current 3.5% of the 500,000 people who die each year, and visitors staying overnight in hospital should pay "hotel charges".

A £10 monthly fee would be used to fund local initiatives to improve prevention of ill-health and an annual "health MoT" for everyone of working age, say Warner and co-author Jack O'Sullivan, an expert in new thinking in health and social care.

The charging proposal immediately prompted a heated debate amongst doctors. One critic dubbed it "as poisonous as the poll tax" while the doctors' union criticised it as "an NHS tax on patients" that would threaten the health service's central tenet of providing care that is free at the point of use.

Dr Clive Peedell, an NHS oncologist who is co-leader of the National Health Action party, said the monthly charge would be "an unfair tax because it's a flat tax and not part of a progressive tax system. The poor would pay the same as the rich. It could be as unpopular as the poll tax was. Politically it's as poisonous as the poll tax." Ministers should instead crack down on the cash lost through tax avoidance and use some of that to boost the NHS's budget, he added.

"Any attempts to introduce what would amount to an NHS tax on patients puts us on the slippery slope towards the end of an NHS that needs to be, and should be, free at the point of use," said Dr Ian Wilson, chairman of the British Medical Association's national representative body.

"The BMA remains strongly opposed to any attempts to introduce charging patients, whether that is a monthly payment, for hospital admissions or for GP appointments."

Social care should be merged with the NHS to create a National Health and Care Service offering patients integrated care. Hospital services should be concentrated in fewer places to improve clinical quality, with closed hospitals becoming primary care centres.

In his article, Warner claims that continuing austerity throughout the next parliament means the NHS cannot get a larger share of general taxation. "Over-protecting an outdated, cosseted and unaffordable healthcare system inevitably means starving other vital public services, unless we choke off economic growth and worsen the cost of living with big tax increases.

"That might all be worth contemplating if the NHS was offering brilliant care. But it isn't," he says, citing poor care of frail, elderly people and high rates of avoidable and expensive hospital admissions.

He attacks the current and previous governments for not tackling the "developing crisis" of affordability in the NHS, and warns that solving the problem will need five years of "continuous political, professional and managerial effort from 2015". Change will involve "political leadership of change, not micro-management of inevitable decline", including backing for Simon Stevens, who takes over on 1 April as NHS England's chief executive, succeeding Sir David Nicholson.

The Department of Health, NHS England and the Royal College of GPs all oppose charging patients for access to care. "The founding principles of the NHS make it universally free at point of use and we are clear that it will continue to be so. This government doesn't support the introduction of membership fees or anything like them," said a spokesman for the Department of Health. "But we know that with an ageing population there's more pressure on the NHS, which is why we need changes to services that focus far more on health prevention out of hospitals."

Meanwhile, a poll of 100 MPs of all parties found 48% believe a free NHS may not survive unless the challenges facing it are tackled, although 65% say there is too little political will to push through the changes needed.

The poll, by Dods Monitoring for the NHS Confederation, found 81% think the NHS in their area needs to change in order to meet patients' needs, but one in four said they would not back a reorganisation if their constituents opposed it.