A developing black market in junk food among children could be the result of the drive to promote healthy eating in schools.

Enterprising children are buying bars of chocolate and packets of crisps in bulk, and making small profits by selling them on to classmates, it was revealed last week.

“You can get a good deal from the boys selling sweets,” says a 16 year old pupil at a respectable comprehensive in south London. “They sell them cheaper than the tuck shop used to.

“Our school has a healthy eating policy, so the shop and the canteen stopped selling crisps and things.”

Following the Channel 4 series Jamie’s School Dinners, in which celebrity chef Jamie Oliver exposed the poor quality of school dinners, many schools have made moves to ban junk food.

Fizzy drink vending machines have been removed, and tuck shops have stopped selling crisps and chocolate. Health campaigners and MPs last week announced that local authorities should have the right to stop ice-cream vans from pulling up outside schools.

But the regime of “gastronomic Puritanism” being imposed on schools will lead to a situation where children will bring in “lunchboxes full of contraband”, according to Mick Brookes, general secretary of the National Association of Head Teachers (NAHT).

“If we want children to eat healthier food, we need to educate their palates rather than going for coercion, regulation and insistence,” he said.

“There is a long history which shows that if you make something out of bounds for children, you only make it more attractive.”