The general election debate over the NHS has already become an exchange of insults, doubtful assertions and unreliable statistics of the kind voters find so unedifying. But despite the noise, both parties are avoiding real discussion of the subject.

Labour has put the health service at the centre of its campaign. The party looks ready to focus on spending the proceeds of its mansion tax – and, of course, on attacking the Tories’ record. But there is no sign of the harder, longer term kind of thinking the previous Labour government was prepared to grapple with. Labour knows the choices are unpalatable, not least with its own voters.

The Conservatives are reluctant to talk any more than they have to about the NHS because they feel no such conversation would end well for them. As I have found in my latest research, which included a poll of more than 20,000 people, and day-long discussions with 80 members of the public, fewer than three in 10 voters think the Conservatives have the best approach to the NHS, 18 points behind Labour – though David Cameron is the only leader thought more likely to care about the NHS than his party does. The Tories fear everything they say will be distorted, and the distortions will be believed.

Some blame the Lansley reforms. I found people assumed these changes had been introduced to save money; more thought they were “part of a plan to privatise the NHS” than to cut bureaucracy or give more choice and control to patients. But it is not as though these reforms tarnished an otherwise gleaming Conservative reputation on the NHS. Rather, in the absence of any clear explanation of how the changes were supposed to benefit patients, people fell back on their assumptions about Tory motivations.

This is because the decontamination of the party brand was never completed. Its modernisation will be complete when it is trusted to sustain and reform the NHS: the matter does not have to be the Tories’ perpetual political millstone.

There is, then, no immediate prospect of a grownup conversation about one of the most important domestic issues of the time – which is a pity, because we need one. Though people were more likely than not to think spending on the NHS had risen in the last five years, they were much more likely than not to think that the service had deteriorated. The fact that NHS funding doubled under the last government, which was news to most people, underlined a view that money was not the whole answer, even if there were any to spend.

While most people’s personal experience of the NHS is good, doom-laden reporting leads them to believe they must be lucky: 78% thought services varied significantly between areas and hospitals.

By far the most popular proposals for raising funds or freeing up resources in the NHS were charging for missed GP appointments (which, if it were ever introduced, would surely raise only a minuscule amount), making bigger cuts in other areas of government spending, and cutting back on non-clinical staff – though as my research also found, people are inclined hugely to overestimate the number of managers and administrators.

Just over half of those polled thought the government should consider using more private companies in the NHS “when they can provide high-quality services more cheaply”. But a fifth, including nearly a third of Labour voters, thought the private sector should not be allowed to provide NHS services “even if this would save money and improve treatment for patients”. Even many of those who had no problem with private involvement in principle feared that shareholders would ultimately be prioritised over patients.

The public was divided over whether publishing detailed information about hospitals, surgeons and survival rates would “raise standards and enable patients to make more informed choices”, or “might be misunderstood by patients and lead them to make choices that are not right for them”.

Indeed only a minority thought choice and innovation were the best way to raise standards; 60% thought the best way was for the government to set targets that all hospitals must meet. While they wanted a uniform service across the country, they also demanded that decisions should be taken by health professionals at a local level to meet the needs of particular areas. Ultimately, only just over half the public expect that in 10 years’ time the NHS will continue to offer a universal service to a high standard. Three in 20 think that in 25 years’ time the NHS will have disappeared altogether.

Discussion of the health service, more than that of most political questions, is laden with emotion: one of our participants described the NHS as “the soul of Britain”. Talking about potential reforms, even when aimed at protecting the service, feels to many like an affront. That is why a proper conversation about the NHS is so important. It’s a shame there is no sign we are going to get one.

Lord Ashcroft’s report, The People, the Parties and the NHS, is available here.