First the Government warned them not to undermine new food standards by putting fizzy drinks and biscuits into their children’s packed lunch.

Then Maurice Smith, the Chief Inspector of Schools, emphasised that children should not be sent to school looking scruffy, or tired from having stayed up late the night before.

For the first time in 25 years junk food will be banned from school dinners, chips will be served no more than twice a week and every meal will include two portions of fruit and vegetables. But head teachers said that the crackdown would succeed only if parents took responsibility for their children’s health.

From September, nuts, seeds and yoghurt drinks will replace crisps and chocolate bars in school vending machines. Locally bought meat and fish will also be served.

Yet while endorsing more healthy eating, heads said that they feared that the tightening of the rules could produce a black market in chocolate bars and crisps in the playground. “Heads are certainly not going to do lunchbox inspections,” Mick Brookes, the general secretary of the National Association of Head Teachers, said. “It is parents’ responsibility.”

John Dunford, the general secretary of the Association for School and College Leaders, said that teachers recognised that a healthy diet promoted concentration and improved achievement, but obesity among young people could not be eradicated by an additional £2,000 of funding to every secondary school with 1,000 pupils over three years. “Schools can offer two portions of fruit and veg, but there is no requirement for students to eat it,” Dr Dunford said. “They can still bring in a packed lunch full of crisps and junk food.”

An Audit Commission report this year attacked the Government for failing to implement measures to curb obesity. In spite of promising to improve school meals since 1997, the Government was only stung into action last year by the celebrity chef Jamie Oliver, who campaigned to ban junk food and demanded more money for school dinners. Ruth Kelly, then the Education Secretary, pledged £220 million over three years. The money was aimed at raising the amount spent on food from 37p per pupil in some schools to 50p in primary schools and 60p in secondaries from last September.

Schools are beginning to source produce locally and offer more organic food. In Essex, 25 schools work with a local farm and the number of pupils eating school meals has risen by 38 per cent. At Christopher Hatton primary school in Camden, North London, Gwen Lee, the deputy head, holds a “vegetable assembly” every week to introduce her pupils to a new food item.

“I look at the menu for the week, pick a veg, promote it and let the children try it,” she said. “They’re really receptive to it and now even prefer parsnips to chips.”

But school is not “a house of fun” and parents need to reinforce the message that children go to learn, Mr Smith, the head of Ofsted, said yesterday.

He told head teachers at a conference in Devon that parental support was crucial for children’s success and the success of schools.

“This means being ready for school, awake and alert, not tired and lethargic from last night’s television, computer or entertainment; being properly nourished and dressed, not scruffy or hitting the sweet shop en route to school for a substitute breakfast; being prompt and enthusiastic throughout the school day, not late or dilatory; being ready to learn — if to confront, to do so with debate and discipline, not ignorance and apathy.”

CHANGING MENU

LUNCH
Out Turkey Twizzlers, fizzy drinks, crisps, chocolate, sweets, deep-fried food
In good-quality chicken, meat and fish; minimum of two portions of fruit and vegetables every day. Chips twice a week

VENDING MACHINES
Out sweets, crisps, chocolate and fizzy drinks, including low-calorie drinks
In nuts, seeds, water, milk, fruit juice and yoghurt

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