More people are unhappy with the NHS than satisfied for the first time in a poll of the public run by Britain’s doctors, and 70% say they think the health service is going in the wrong direction.

The growing public concern will be revealed by Dr Mark Porter, leader of the British Medical Association, who will tell his annual representative meeting in Bournemouth on Monday that the government is “trying to keep the health service running on nothing but fumes”.

Porter, in his last speech as BMA council chair, will say the health service is at breaking point. “It doesn’t have to be this way. It is the result of an explicit political choice,” he will tell the meeting.

“We don’t have to spend less of our GDP than the other leading European economies on health. Our government has chosen to do this. If we spent the average – the average, not the most – then patients would see £15bn extra investment in the English NHS within five years. We’re not asking for the world. We’re asking for the average. For a fair chance to create the health service our patients need and deserve.”

He says the public are being “belittled and bewildered”. The government wants a world-class NHS but is only offering it a “third-class” financial settlement, he claims.

The British public has always overwhelmingly supported the NHS and had positive views of it, but the BMA poll suggests that may be in danger of changing. While the data came from an online survey of a relatively small sample of 1,031 adults living in England, there has been a marked erosion of satisfaction since similar polls in 2015 and 2016.

The latest poll shows 43% of respondents are dissatisfied with the NHS, and 33% are satisfied – a doubling of dissatisfaction in two years. In 2015 a BMA survey found that 21% were dissatisfied, with 56% saying they were satisfied. In 2016, 37% reported that they were dissatisfied, with 41% satisfied.

The poll also shows that 82% are worried about the future of the NHS, while nearly two-thirds (62%) expect the NHS to get worse in the coming years, compared with 39% in 2015. Only 13% think the NHS will get better, compared with 26% in 2015.

The leading concerns are lack of funding (50%), the possibility that the NHS may cease to be free at the point of use (41%) and that waiting times will increase (35%). Almost seven out of ten (69%) think the NHS will not get sufficient attention because of Brexit.

Dr Mark Porter, head of the BMA, will tell the meeting ‘the NHS is failing too many people, too often’. Photograph: Frank Baron/The Guardian

“Prime minister - you ignore the NHS at your peril,” Porter will say in his speech. “We still have one of the best healthcare systems in the world. It treats more patients than ever before, and deploys treatments of which I could only have dreamed when I qualified as a doctor. But after years of underinvestment, with a growing, ageing population, and despite the extraordinary dedication of its staff, it is failing too many people, too often.

“It’s not just doctors saying this. According to research we have published today, 62% of the public think the NHS will get worse over the next few years. Two years ago, that figure was 39%. Our research shows that the public expects waiting times to rise, the scope and availability of services to contract, and that the NHS will not receive the funding it needs to deliver high-quality care. For the first time in our polling, more of the public are dissatisfied with the NHS than are satisfied.”

A small additional survey by the BMA of 422 doctors shows 71% believe accessing care has become more difficult for patients over the last 12 months. Among hospital doctors, 65% have vacancies in their department, while 48% of GPs say there are unfilled posts at their practice.