Obesity surgery is the ultimate ambulance at the bottom of the cliff. It exists for those who continue with an unhealthy lifestyle even when they know they are over-eating and are not exercising regularly. Such a failure of personal responsibility means this form of surgery - sometimes referred to as stomach stapling - will always be controversial. Spending taxpayer's money on it will be opposed by many. To such people, increased Government spending suggests only an escalating tendency to park the ambulance in the wrong spot.

Associate Health Minister Tariana Turia has announced a four-year, $2 million increase in state funding for bariatric surgery, which she says will mean up to 300 extra operations. This equates to an increase of more than a quarter on the number now being done. Mrs Turia herself paid to have bariatric surgery done privately last year. About 400 people a year, including Anne Tolley, now the Education Minister, and fellow National MP John Hayes, do the same. Many of these cases, however, would probably come under the umbrella of cosmetic rather than obesity surgery.

Government funding should be reserved exclusively for the morbidly obese. In their case, a measure that is drastic in nature can be justified on the basis of long-term savings to the health system. Frequently, for example, bariatric surgery terminates diabetes in patients. But it should also be exclusively for those who demonstrate a willingness to change how they eat and how they exercise. No operation provides the complete solution and there must be the prospect of the best-possible result from taxpayer funding. In that regard, the Counties Manukau District Health Board is on the right track in dictating that not only should diabetes be one of the selection criteria for surgery but that people must have proved their weight-loss motivation by losing 5kg to 10kg.

Bariatric surgery, which reduces appetite and the amount that can be eaten, is not cheap. The cost for each operation ranges from about $15,000 to more than $20,000. That will keep increasing as more-sophisticated and complex techniques are introduced. It is important, therefore, that there is no slippage in what qualifies individuals for surgery. People who want the operation largely for cosmetic reasons should be left in no doubt that they will still have to pay for it in a private clinic.

Labour's health spokeswoman, Ruth Dyson, is right to suggest there is an irony in all this. While the state is increasing spending on obesity surgery, healthy-eating programmes are being cut back. The latter, of course, represent the ambulance at the top of the cliff, and the increasing cost of obesity to the public purse provides every justification for health officials to seek and encourage improved eating and exercise patterns.

In particular, parents need to be educated and informed, and be prepared to encourage their children to be more physically active.

This holds the long-term key. Children's diets have not deteriorated markedly, while the obesity rate has accelerated. What has changed is the amount of time they spend in front of television, playing computer games and trawling the internet. No longer, either, do they walk or cycle to and from school.

The prevention of obesity must be at least as much a part of the response to this growing problem as treatment.

Bariatric surgery may be justified in some instances, and have a dramatic impact on an individual's health and wellbeing.

But such taxpayer-funded operations should be kept under a tight rein. Otherwise, the wrong signal is being sent.