"The procedures could leave the already strained NHS with a £12BILLION bill"
Eating disorders exist in developed countries where food is abundant. There is not an obesity problem in countries where food is scarce. Anorexia is a psychological problem. Obesity is also a psychological problem.
For someone to consider surgery a practical and sensible choice instantly identifies them as having a mental illness. For a person to be unable to recognise their growing body fat, or diminishing body weight identifies a mental illness involving delusion and a self-perception misfire in the brain.
Eating disorders are a symptom of societies with food abundance. Abundance of food products that are processed and produced in what look more like laboratories rather than kitchens. The over fat and the under weight are not part of any social group. Many are successful in life and work and education. Many have otherwise productive lives. It is not an illness of the ignorant or the uneducated.
Eating disorders are a pyschological mental illness. In short, the person is so compelled to eat, or starve, that the sense in what they are doing is pushed aside. Sense, that is, in terms of the risk to their existence. Deliberately starving yourself is only going to end badly. Over eating, sooner or later, is only going to end badly. Even if it doesn't end badly, the path to the end is an uncomfortable path.
The gastric band stops food from entering the guts, as far as I know. People feel fuller quicker when they eat. This curbs appetite and thus intake of calorie volumes. So it is probably fair to say that it works. And the return on investment may be a viable argument too. Nip it in the bud now, and save on monstrous medical bills when that patient becomes the long term sick.
The fact remains, however, that a doctor recommending surgery for a psychological disorder is akin to the archaic practise of electric shock treatment in asylums in previous centuries.
In my experience of mental health the only thing doctors are good at is dishing out drugs. Uppers, downers and all sorts of other poisons that turn thinking people into stoned zombies. Indeed, there was a time when amphetamines were dished out as appetite suppressants.