Pupils are not eating healthily at lunchtime because of pressures on school dinner budgets, a teacher has warned.
Junk food is one of the main options for school children
The deputy head of a west London comprehensive, who asked not to be named, said children were not being offered options such as salads and fresh fruit, because of high costs.
Instead, most were choosing from a range including pizzas, burgers, chips and crisps.
The deputy head said: "I wouldn't want to blame the catering company. It does the best it can in the circumstances.
Crisps and chocolate
"But the choice on offer is limited by finances."
The school's catering company receives £1.32 per day for each child entitled to a free meal.
They, and others whose parents pay, are given swipe cards to use in the canteen.
The children have a choice of three types of meal. The first is more traditional food, like roast dinners, pasta and curries.
A second area serves fast food, like burgers and chips.
The third - called a "snack shack" - provides crisps, chocolate and similar items.
The deputy head said: "The problem is that the company is operating within such a limited budget.
'Difficult for caterers'
"Healthier food, like salads, tends to be more expensive to provide and is more perishable than lots of unhealthier options.
"We try to encourage pupils to eat better food in the appropriate lessons.
"But it's difficult for caterers to follow this up, however imaginative their solutions. They have to cover staffing and energy costs out of the money they get."
The poorer children were suffering most, the deputy head said.
"Some of our more middle-class children are exposed to a wider range of foods. They often get a healthier meal at home.
"Some of our students wouldn't dream of eating school meals, They often bring their own lunches, containing salad and other nutritional food.
"But others are not getting a healthy meal, either at home or at school."
Martin Ward, deputy general secretary of the Secondary Heads Association, said: "Often, there are limited number of companies going for contracts to supply school dinners.
"The companies come under a lot of pressures. When I was a principal, we had to change the contractor because of the quality of food provided.
"A lot of bigger schools are better placed to provide meals themselves, rather than farming out contracts to companies."
Government nutritional standards for school meals were introduced in 2001. All previous regulations had been abolished in 1980.
But a study for Which? magazine earlier this year found diets were typically lacking in vital nutrients such as iron, zinc, protein, calcium and vitamins A and C.
They were, however, high in saturated fat, sugar and salt.
The government advises that eating five portions of fruit or vegetables a day can help reduce the risk of heart disease and cancer.
School meals contributed less than 1.5 portions on average, Which? found.