Consider these benefits. Improved performance from better-behaved children.

A consistent curriculum that makes a greater impact. A younger generation protected from diet-related sickness and obesity. A smaller health-tax bill for everyone. Then imagine pupils who chat over breakfast or lunch in a smart school cafe rather than roam the high street snacking on crisps.

Children who appreciate that they are valued and respected and respond in kind. More money for the school - and less for multinationals such as Nestle and Coca-Cola.

“How many things do you want out of a package before you realise its value?” asks Joe Harvey of the Health Education Trust, a one-man pressure group. The package, put simply, is better food for children. The Government is on board, he says, because it is alarmed by the prospect of huge health bills courtesy of an overweight junk-fuelled generation with high blood pressure and furred-up arteries. Just one statistic reveals the extent of the problem: in 2002, children aged eight to 16 spent pound;433 million on sweets, chocolate, crisps, gum and cigarettes on their way to school, a 68 per cent increase on the 1998 figure.

These children could be in school eating a healthy breakfast.

Caterers, be they in-house, local authority or private, risk losing more of their customers who spend about pound;1 billion a year just at lunchtime.

An estimated 39 per cent of UK pupils never eat a school meal. They hate the queues and the cramped dining halls. But there are obstacles. A long-term lack of investment in equipment and staff training is one. The varying value of a free school meal which should act as a national benchmark is another. And skimping on the cost of the ingredients themselves is a third.

“We must challenge the investment level and the fluctuation of the value of a free school meal,” says Mr Harvey. “We are not talking big money here.

The Government only pays for free meals; the rest is paid for by the customer. These are simple things, but they have to be done in a whole and intelligent manner, with the Government setting expectations, and the inspectors checking on the results.”

Inspectors have just added “food education” to their checklist, but schools should not wait on their advice. They can already challenge the status quo of children surviving on chocolate for breakfast, indifferent canteen food for lunch, and an afternoon helping of vending-machine junk. They can already provide a principled and high-quality food service, says Mr Harvey, particularly since the budget was delegated to secondary schools and made an option for primaries.

Success depends on ensuring that the message children get at school is consistent - and healthy. There should be no contradictions between what they are taught about food through the curriculum, what they cook (if they do), what they buy from vending machines, what they eat for breakfast and lunch, and what they nibble on for a break-time snack. Success also depends on setting up a partnership involving the head, staff, governors, caterers, parents - and crucially the pupils themselves.

Mr Harvey has pioneered the concept of a School Nutrition Action Group (or Snag). The group, which includes all members of the partnership, then implements a whole-school food policy. This approach is backed by the Department for Education and Skills which says that about 4,000 schools are signed up to the Healthy Schools eating strand. Examples of good practice are being researched by the Food Standards Agency and the Department of Health through its Food in Schools programme. Yet only about 12 per cent of schools have - or are planning to set up - food groups, according to Sodexho, one of the biggest catering concerns in the country.

Among those 12 per cent is the Teign school, in Kingsteignton, Devon. Last year it set up a health forum giving a voice to older students as well as teaching and catering staff and governors. New menus were drawn up as a result of a nutrition review and the canteen was revamped. Dishes now on offer include ratatouille wraps, ham tortellini, roast dinners, and tuna pasta bake. A milk bar adorns the new cold food area.

High-sugar drinks, chocolate, and sweets are no longer sold in the canteen as “they did not always put the best background on behaviour”, says Kingsley Matthews with understatement.

Mr Matthews, the school’s administrator, was a key figure in the review. He says Teign students have reacted favourably to the changes. A few snacks such as chocolate biscuits and crisps can still be bought through vending machines, but students need cash for those - everything else is purchased using smart cards - and the hope is that this will be a disincentive. In the canteen, chips and other fatty dishes have become more expensive while healthier items are priced as keenly as possible.

The health forum is set to evolve into a Snag, with representatives from all year groups. “Their ideas are essential and often very good,” says Mr Matthews. “We want feedback from students, parents and staff. You can’t always do everything, but at least there is a forum for debate.”

The headteacher, Alan Pritchard, believes better food has a direct link to better results, but that is not the only reason for improving pupils’ diet.

“Schools are about more than academic performance,” he says, “and we can hopefully help sow the seeds for our students to enjoy an active and healthy adult life through the changes we are making now.”

The road to a quality service requires commitment. A Cambridgeshire secondary just embarking on the journey has so far achieved a day a week without chips. “I know it sounds pathetic,” said a spokeswoman, “but at least it is a start.”

Joe Harvey is an evangelist: “There are very few challenges to working towards a whole-school policy on food and nutrition that cannot be overcome with intelligence, determination and a positive attitude to partnership working - and we can help you hatch a cunning plot.

“You have got to turn round the people who actually hold the budgets, work on the basis of principle and partnership, set sensible, simple policies, and involve your students because it is educationally sound to do so - and because you cannot run any good business of any kind where the person producing the service ignores the customer. You will get huge benefits.”

There is, then, only one problem left, says Kingsley Matthews of the Teign school.“I just daren’t go to the canteen too often or I’ll get too fat.”

GET HELP

The British Nutrition Foundation www.nutrition.org has a detailed and downloadable guide on setting up a whole-school food policy on its website , drawn up with the help of the DfES. The Health Education Trust www.healthedtrust.com is another source of help. It also publishes “The chips are down: a guide to food policy in schools.”