Kicking a football around for just 15 minutes a day can halve a child’s risk of becoming obese, a study has found. Even small increases in daily activity, such as walking to school instead of going by car, could have impressive long-term results, researchers say.

The official advice is that children need an hour of moderate to vigorous exercise a day - long enough to put off many parents who do not have the time to take their children to the sports centre. But a quarter-of-an-hour’s kickaround may be all that is needed, according to the University of Bristol team.

The finding comes as figures show diseases attributable to lack of exercise cost the NHS more than £1bn a year. Heart disease, breast and bowel cancer and diabetes, which are associated with low activity levels, together claimed 287,000 lives in 2003-04, according to researchers at the University of Oxford.

Writing in the Journal of Epidemiology and Community Health, they said 35,000 of the deaths were directly attributable to physical inactivity and the financial burden on the NHS of caring for the casualties created an “economic case for developing policies and interventions that promote physical activity”.

The extra activity required may be less than many people have thought. Researchers who monitored 5,500 12-year-olds from the Children of the 90s project, based at the University of Bristol, found that for every 15 minutes a day spent in physical activity, equivalent to a brisk walk, the chances of being among the top 10 per cent of fattest children was almost halved.

The boys spent an average of 25 minutes a day engaged in moderate or vigorous activity. For girls, the average was 16 minutes a day. Activity levels were measured by attaching a monitor to a belt around the waist. Body fat was measured using a low-dose X-ray scanner. The study is published in PloS (the Public Library of Science), an online journal.

Professor Andy Ness, of the University of Bristol, said: “It has been really surprising to us how even small amounts of exercise appear to have dramatic results. If you say to parents they have got to take their children for an hour-long early morning run, they will throw up their hands and say it is impossible. But if you say kicking a ball around for 15 minutes or going for a quick swim is all that is needed then they may well feel that is manageable. And it is probably good for the family, too.”

Professor Ness said girls were no more likely to be obese than boys and that their lower activity levels indicated they were using “other strategies” to stay slim, such as “dietary restraint”. But claims by rival researchers that activity levels of children were genetically pre-determined were wide of the mark.

The Children of the 90s study has monitored 14,000 children born in the Avon area in 1991-92 alongside their parents. Rates of childhood obesity rocketed in the 1980s and early 1990s. Around a quarter of British children aged 11 to 15 are now overweight or obese.