Anyone who doubts the power of homeopathy may want, its practitioners point out, to account for an extraordinary longitudinal study involving multiple generations of one exceptionally long-lived British family of homeopathy enthusiasts.

Even allowing for other life-extending factors, such as footmen, normalised indolence and a morning pint or so of gin and Dubonnet, the propensity of so many Windsor-Mountbattens to survive into their 90s and, in the late Queen Mother’s case, much longer, is so striking that homeopaths are understandably eager to accept responsibility. They “live long and healthy lives,” says a member of the School of Homeopathy, presumably attributing to chance the marginally less inspirational example of noted homeopathy enthusiast, George VI (1895–1952). With every comment on their prodigious health, the Queen, aged 91, and her husband, 96, become a yet more valuable promotional asset to advocates of Hahnemann’s potentisation. The same, admittedly, applies to passionate advocates of never running your own bath. Either way, the royal family’s importance in promulgating homeopathy, by way of physical evidence, as well as through their official patronage, perhaps justifies what might otherwise appear intrusive inspection of their respective physical states.

What, for instance, did Prince Charles mean by his recent pleasantry, addressed to fellow almost-70-year-olds, to the effect that “bits of me keep falling off at regular intervals”? Which bits? It was encouragement enough for royal correspondents to list various health problems, from a bad back to finger difficulties, which might be 20 times worse if the prince were not a lifelong homeopathy patient. Or 20 times better. Or, given homeopathy remedies have no active ingredients, exactly the same. As with so many homeopathy trials, there is no control prince.

Still, so long as he remains more or less functioning, homeopaths can reasonably hope, now that it has been announced that Charles will succeed his mother as head of the Commonwealth, that he will be as determined to promote quackery among the other 52 nations as he has been within the UK. If NHS doctors are still – as it was confirmed last week – offering treatment described by the chief medical officer as “rubbish”, by the head of the NHS as “at best a placebo and a misuse of scarce NHS funds”; and by NHS Choices as not “consistent with long-accepted principles on the way the physical world works”, then the credit for this achievement should surely go, almost if not quite entirely, to the Prince of Wales.

Facebook Twitter Pinterest Christian Hahnemann, founder of homeopathy. Photograph: Hulton Archive/Getty Images

It would be wrong, after all, to overlook the contribution of some prominent MPs to preserving the memory of water theory from the constant threat from evidence-based medicine. Jeremy Hunt finds a homeopathy-friendly ally in, for instance, Jeremy Corbyn. Although where some compounds are concerned, a noted stickler for evidence, the leader of the opposition is minded to exempt homeopathy – for which royal partiality remains, perhaps uniquely in the NHS, a critical evidence base.

As well as supporting early day motions in favour of homeopathy, Corbyn tweeted, in 2010: “I believe that homeo-meds works for some ppl and that it compliments ‘convential’ [sic] meds. they both come from organic matter…”

That would be “come from”, in the sense of diluted-to-the-point-of-not-being-there-any-more, with the original “organic matter” being selected according to the magical principle of “like cures like”.

As for “works for some ppl”, this has recently been demonstrated by a Canadian practitioner, Dr Anke Zimmermann, who described how she cured “Jonah”, a four-year-old exhibiting aggression, with a remedy derived (like curing like) from the saliva of a rabid dog. “Within a minute or two of giving him the remedy,” she reported, “Jonah smiled at me very broadly and beautifully, as if all the lights had just gone on.” Following widespread criticism, an indignant Dr Zimmermann now emphasises that homeopathic remedies are “harmless sugar pills medicated with sth [something] like an energetic information of the substance”.

Possibly because of stories involving rabid dog saliva, along with a growing reluctance to spend public money on this energetic information of the substance, the use of homeopathy has been declining within the NHS, to the point that in 2017 it finally proposed a ban on prescriptions. It will certainly require more than damning surveys, to judge by a new study, to deter a still active body of NHS-based Hahnemann enthusiasts from prescribing remedies from the same pharmacopeia as the rabies cure.

The study, published in the Journal of the Royal Society of Medicine, may make, within the homeopathic community, for bittersweet reading. Researchers, led by Ben Goldacre, senior clinical research fellow at the University of Oxford, found that determined GPs, in over 600 surgeries, were still, regardless of the official “rubbish” verdict, prescribing homeopathic remedies in 2016-2017. However, the relevant surgeries were also shown to be less competent, on all the accepted prescribing measures.

A willingness to defy the principles of evidence-based medicine like this is shown to accompany other examples of poor prescribing. If it’s over-harsh to summarise the homeopathy prescribers, as one report did, as “bad doctors”, it’s reasonable to ask how these professionals reconcile the existence of Nice’s guidance on evidence-based decisions with the prescription of, say, potentised bee venom, presumably out of personal conviction. Is it so much better, really, than branding your initials on a transplanted liver, because, as that surgeon said of his (mercifully harmless) misconduct:“I do this”? He was fined and sentenced to 120 hours of community service.

Homeopath-GPs, naturally, have mustered in response and challenge Goldacre’s findings, with a concern for methodology that could easily give the impression that there is some evidential basis for their parallel system, beyond the fact that the Prince of Wales likes it. In fairness to Charles, his upbringing is to blame. But what is the doctors’ excuse?

• Catherine Bennett is an Observer columnist