Schools are pressing parents to discourage children from visiting corner shops at break times in case they buy sugary or fatty snacks, according to independents.

Nigel Mills, MD of leading independent Mills Group, which owns 75 stores and is based in Tyne & Wear, said: "One school in our territory has written to parents saying could their kids please not call in at newsagents and c-stores during breaks because their sweets make them hyperactive."

He was unfazed, because Mills Group had introduced grab and go sandwiches and healthy food into 30 stores. This was driving impulse confectionery sales down in those stores, but sales of healthy options had risen.

A spokesman for the Department for Education & Skills said such action by schools was not part of a government initiative. But individual schools were free to implement their own practices based on School Food Trust guidelines.

The SFT said it was unaware of schools writing to parents but added: "We're aware of schools working with local shopholders to provide healthy alternatives and educate children about balanced diets."

Government rules on healthy eating in school lunch breaks began to take effect last month. Further rules on eating outside the lunch hour, which will crack down on sugary or fatty products in school vending machines, are to be implemented next September.