Scottish head teachers are demanding changes in the law, so that children stay at school during lunch breaks instead of taking the 'chip shop run'.

In a bid to improve youngsters' eating habits, heads say legislation should be introduced to ban mobile chip vans and other sellers of snack food from operating outside schools during the working day, reports the Scottish daily Scotsman.

The 'chip shop run' is the quick visit students make to the nearest chip shop or fast food joint in town, during the lunch break.

Bill McGregor, general secretary of the Head teachers Association of Scotland, said: "We would like to see legislation to make it more difficult for children to get at the chip vans around the school gates. These people are part of the problem that leads to a poor diet at school."

McGregor added that he also backed any plans to crack down on the current 'open-door policy' at schools during lunch hour.

Heads, at present, are only able to keep children in school if parents expressly ask that they be banned from leaving, whereas in England, schools are allowed to keep pupils behind the school gates.

Despite the head teachers' call, the Scottish Executive has no plans to revisit the laws. Ministers are instead focussing on trying to make school canteens more attractive for pupils.