Children are shunning the school canteen in favour of cheap junk food, according to research.Secondary school pupils enjoy the healthy meals introduced by chef Jamie Oliver but are having to pay too much and wait too long to be served inside crowded canteens, researchers from London Metropolitan University found.Expense and poor facilities are undermining efforts to overhaul the diet of UK students, the report concluded.The study of pupils found 80 per cent bought food from local shops, 41 per cent never went to the school canteen and just 6 per cent ate the school's set hot lunch.Researchers from the university's Nutrition Policy Unit observed the food shopping habits of pupils at two large comprehensives - one in a deprived urban setting and another in an affluent suburban area.Professor Jack Winkler, the co-author of the report, said: "Our research found that local takeaways in the school fringe were undercutting the school canteen by offering child-sized portions for £1."This meant that for the equivalent price of a school meal, pupils could buy chicken and chips or a whole pizza and still have money left over for a drink or sweets."