The TES has seen the full report on a pilot scheme in Hull primary schools that gave free meals to pupils, irrespective of their background, from 2004 to 2007. The report concluded that the lunches improved pupils’ behaviour, social skills and academic results.

Ed Balls, the Children, Schools and Families Secretary, and Alan Johnson, the Health Secretary, are now to meet the Hull University academics who evaluated the programme to discuss their findings.

Hull’s experiment, called “Eat Well Do Well”, provided free meals to about 25,000 pupils.

By the final year of the initiative, more than half the teachers reported a positive impact on pupils’ energy levels, powers of concentration and punctuality.

One headteacher told the researchers: “I can now actually spend lunchtimes talking to staff about educational issues, rather than dealing with problems of behaviour in the playground.”

Researchers found that the programme had a “significant impact” on children’s perceptions of healthy food. The study also showed the re-introduction of charges last September had “a negative impact on schools, children’s behaviour, families and opportunities for learning”.

Under the free meals initiative, children were provided with healthy breakfasts, hot lunches, an after-school snack, and fruit up to key stage 2. Nationally, free fruit is only given to pupils in key stage 1.

School staff and pupils from Years 4, 5 and 6 were asked for their views throughout the scheme. By the final year of the experiment, 58 per cent of teachers and teaching assistants said they had noticed a difference in their pupils.

More than four in 10 said the children had more energy, and more than a quarter reported fewer behavioural problems at lunchtime. Only 4 per cent of staff suggested the scheme was not a good idea.

However, the impact of the free meals on key stage 2 results has not been evaluated, as Derek Colquhoun, the professor leading the study, considers the tests unreliable.

The initiative also had a positive impact on children’s diet. “The results show clear evidence of a decline in many ‘bad habits’; eating on the way to school; not having any breakfast; not having an evening meal and going to bed feeling hungry,” the report said. By the end of the three years, researchers could not differentiate between children from poorer and better-off backgrounds in their attitudes to food.

The free meals became more popular in time. Take-up was 86.5 per cent in the first year, dipped in the second year but rose to 94.8 per cent at the end.

Despite the scheme’s successes, ministers may be deterred from implementing it nationwide because of costs. Hull council dropped the scheme, saying it could not afford the annual pound;3 million bill. Since the reintroduction of charges at pound;1.10 a day last September, take-up has fallen, as lower-income families revert to packed lunches.

The Government has committed more than pound;600 million between 2005 and 2011 to the overhaul of school lunches following the high-profile campaign by celebrity chef Jamie Oliver against the use of cheap ingredients and junk food.

Some local authorities were spending only 40p per meal, although that has now gone up to 60p in primaries, and more than 70p in secondaries.

But according to the School Food Trust, the take-up of school lunches has fallen since the introduction of tighter nutritional rules.

A MENU TO DIET FOR

What was cooking the week that researchers visited Hull schools

Monday: Spicy beef with rice and pitta bread, carrots, broccoli, sugar-free jam, a scone, and apple juice.

Tuesday: Roast turkey with stuffing, boiled potatoes, green beans and carrots, tomato and herb bread, a fruit cocktail, and a glass of milk

Wednesday: Jacket potato with tuna, cauliflower and cabbage, tomato and herb bread, semolina, plus water.

Thursday: Lemon chicken, tomato pasta, broccoli, cauliflower, bread, yoghurt, and a glass of orange juice

Friday: Haddock in breadcrumbs, boiled potatoes, peas, sweetcorn, bread, fruit mousse and crumble topping, and a glass of apple juice.