Scotland’s political leaders are so pleased with their six-week-old smoking ban, they have moved swiftly on to the next public health target: children’s diets. In a bid to tackle childhood obesity, ministers are to outlaw all junk food and fizzy drinks from schools.

Under the Schools (Nutrition and Health Promotion) (Scotland) Bill, education authorities will have a legal duty to ensure food and drink supplied in schools meets nutritional standards. (There will be an exemption for chips, but more of that later.) The ban will cover school dinners and vending machines, which will have to replace crisps, sweets and chocolate with healthy snacks.

Clearly, the executive, emboldened by smokers’ obedience, is on a roll. If it can stop diehard nicotine addicts from smoking simply by passing a law, surely it will be easy-peasy to make fat kids thin.

Certainly, something needs to be done. In December, it was revealed that the number of obese children here was double the UK average. Scotland’s youths are even more obese than their counterparts in America. More than a third of 12-year-olds were overweight in the last school year, with 19.4% obese and 11.2% severely obese. Toddlers, too, were showing alarming signs of weight gain, with 20% of three-and-a-half-year-olds overweight.

These children face a lifetime of ill health related to their size, and the scale of their malnutrition is unacceptable in an allegedly grown-up western society. But their problem cannot be cured by legislation. Bad eating habits, like smoking habits, have to be addressed through education.

The ban against smoking in public places has not eradicated smoking, as any stroll along any high street or past any office block will confirm. Smokers not wishing to flout the law and pay a fine continue to smoke, but do so outside, as early findings by cigarette manufacturers confirm.

A ban on junk food in schools will not stop children eating junk food. They will still swig coke for breakfast en route to the classroom, go on the chip run at break, and guzzle crisps in between.

Peter Peacock, the education minister, insisted that the new plans “build on the success already seen. By ensuring that all food and drink in schools is healthy and nutritious, we are making it even easier for children to stick to the healthy options.”

Chips, he said, could be excused because they were harmless if eaten once a week.

Oh, how naive he is! On the BBC news the day of the junk-food ban announcement, Peacock spoke earnestly about the “sophisticated” and “mature” choices children now made about what they eat.

Has he never been in the vicinity of a school at lunchtime?

If the evidence before our eyes were not enough, statistics show that fewer children eat school dinners now than before the executive became interested in them. Apparently they have been put off by “healthy options”.

All the evidence suggests the vast sums of money thrown at childhood obesity have had no effect. Three years ago the executive launched its £60m Hungry for Success programme, which hands out free fruit in primary schools. Publicly funded fat and fitness czars have been installed. Two years ago Jack McConnell confessed to a vegetable-free childhood and threw his own weight behind a five pieces of fruit a day initiative.

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