Blessed are the cheesemakers. Outside the cookery room on the first floor of Duchy Manor middle school, a student brushes past, clutching a bundle of muslin. “Sniff my cheese,” she says. “It’s really mouldy.” Ah, such pride in one’s work.

Inside, pupils are kneading dough ready to bake their own bread. But the real action is in the car park - in the Cooking Bus. It’s there you can feel the real heat of the ovens and watch the headteacher, Gerry Hillman, and his wife don pinnies and sink their arms up to their elbows in the washing-up bowls.

The culinary pantechnicon is in the quiet Wiltshire village of Mere for Duchy Manor’s food week, spreading healthy eating messages, encouraging good hygiene and, most important, promoting the joys of home cooking. The Cooking Bus is the Focus on Food campaign in action and a marvel of engineering. On the move, it’s a simple lorry trailer, hauled by the affable Paul, who sleeps in the cab. Once parked, its sides fold out to create a classroom twice its size.

Inside, four brightly coloured worktables are surrounded by half-a-dozen hobs and ovens, sinks with their own 500-litre water supply and cupboards piled high with dozens of chopping boards, mixing bowls, wooden spoons and spatulas, saucepans and rolling pins, baking trays and cookie cutters, and enough sharp knives to make the most cynical celebrity chef weep. In the fridges at the back, you could just about slide a lettuce leaf between the potato cases, bottles of milk, trays of eggs and fresh fruit and veg.

There’s a box of plasters (though accidents are surprisingly rare), and industrial quantities of cleaning fluids.

The bus is big on hygiene: wash your hands, wear your apron, tie up that hair. No rings, no bangles, no nail polish and definitely no poking your ears or playing with your fringe. And like any kitchen, it’s only as good as the washers-up. Which is why every school it visits is expected to provide an army of soapy volunteers, from mums and dads to the headteacher.

That way the pupils can get on with the important stuff.

In the bus this morning, they’re making salmon bridies and stuffed potatoes, sponge cakes and a jug of the tangiest lemonade I have tasted in a while.

Focus on Food is a Royal Society of Arts initiative which is sponsored by Waitrose, the supermarket chain. Its mission is to improve cooking in schools, and beyond that to encourage a healthy attitude to food. The bus, which travels about 10,000 miles a year, is so popular that schools have to wait months for a visit. Now, courtesy of the Food Standards Agency, a second pantechnicon is to take to the road.

About 7,000 pupils every year turn recipes into food on the bus. But children are not the only target. Focus on Food’s director, Anita Cormac, says training is the biggest challenge. “The majority of primary teachers haven’t had any training at all.”

Then there is the lack of facilities. “In our estimation, maybe 12, maximum 15 per cent of primaries have purpose-built areas, and they’re quite small.

That’s a big barrier.”

Cooking has suffered in schools since 1992 when it became optional at key stage 3. The campaign would like to see ingredients nationally funded and cooking lessons inspected as a sign that the Government takes the subject seriously. The situation is better than perhaps five years ago, Ms Cormac says. But for many families, it’s already too late.

“We’ve actually lost a generation of young people who can’t cook. Those young people now have children of their own so we’ve got a perpetuation of a ready-meal culture, of people who don’t know and don’t have the inclination.

“We’ve lost our loving relationship with food in a way. We’re very influenced by America - we’ve grown to equate huge portions with good food.

Families don’t eat together; we all eat in front of the TV. On the Cooking Bus, we see children who can’t use a knife and fork. It’s a reflection of the fact they eat chicken nuggets at home.”

Inside the bus, the heat is rising as the potato skins stuffed with a cheesy mix of tomatoes and peppers go in the oven. The bus today is big on spuds. Teacher Ann Kerry asks the group, “Who likes potatoes?” - every hand shoots up. Ms Cormac tells of a class in Scotland where only two-thirds of the pupils responded. The others were mad on chips and crisps, but didn’t realise where they came from. Even in this traditional farming territory, these Year 6 pupils aren’t completely at one with the land.

“What’s this?” asks Ms Kerry, holding up a leek.

“ErI celery?” comes the tentative reply.

Still, the pupils in this class say they like a good roast, complete with swedes and cabbage and broccoli, and turn their noses up at fast food and chips.

Georgie, 11, looks faintly disgusted: “A lot of kids at this school have chips every day.”

Christy, 11, likes spaghetti bolognese and says she’s had McDonald’s only twice in her life. “My mum doesn’t like me eating fatty foods. But I still get fat.”

Yet Christy is not fat. Ms Cormac says: “I’ve had children in some schools asking about the Atkins diet. I find children concerned about their image from a very early age. They’ll often say they’re on a diet - I find that very worrying.”

Sue Dawson, Duchy Manor’s food co-ordinator, worries that many children miss breakfast, and says colleagues notice pupils’ concentration wavering in the afternoons if they don’t eat a proper lunch. “Children need to know about healthy diets, and how to cook for themselves, and that it’s cheaper and more nutritious to prepare their own food, as well as more satisfying.”

Pupils get only one term’s cooking a year as part of design and technology, in a small kitchen where not everyone can cook every week.

So teachers have cleared the whole timetable to make a week of it, with trips to trout and cattle farms and visits by an organic co-operative, a cheesemaker and even an apple farmer who brought his own apple press.

To complement this focus on local produce, the teachers on board the Cooking Bus are teaching some good old-fashioned British recipes. At other times, in other places, they might help schools celebrate Chinese new year or Diwali. It’s about celebrating the social aspects of food, as well as pushing the Government’s five-fruit-and-veg-a-day message.

Focus on Food backs the whole-school approach, going beyond the classroom to encouraging healthy meals in the canteen, sugar-free drinks in the vending machines and, if possible, a ban on junk food pushers in burger vans outside the gates.

The more innovative primaries realise that cooking fits right across the curriculum, from science - all that mashing and melting, all those changing states - to maths. Children have cooked curries for geography and improvised on Second World War rations for history. And what could be a better PSHE skill than cooking?

“When they leave school, these children will have the skills to be able to buy food and cook from fresh raw ingredients,” Ms Cormac says. “Gone are the days of boiled pasta and tomato paste as a student dish,” she says.

Some students spend up to pound;40 a week on takeaway meals, then wonder where their money has gone. “We’re concerned about young people who don’t have the skills because they’ve got no choice but to rely on ready meals, which are expensive and high in sugar and salt.”

But it’s not only the charity that is concerned. “Every July we take calls from worried parents who want a summer school for their children going off to university. And we get another spate of calls at Christmas, when their children come home overweight or drip-white and thin.”

If only they knew how to bake their own stuffed potatoes - and make their own smelly cheese.