Manchester United manager called for a more "rounded" education

In a book financed by the government, he claims inactivity and over-eating are leading to a generation which lacks "basic athletic skills".

Sir Alex, 62, said: "We have got to get sport back into our schools.

"I am sure there are problems with teachers giving up their spare time to run teams, as well as schools being able to find the resources for pitches and equipment, but it's my view that an education is not rounded unless it makes provision for sport."

'Timebomb'

The comments come as concerns are rising over the amount of exercise children get.

Computer games and television are drawing many away from sport, while fewer are walking to school.

Government figures show the level of physical activity in schools has fallen by 70% in the past 30 years.

Meanwhile, young people get on average less than 90 minutes' exercise a week, according to the British Nutrition Foundation.

As a result of this and changes in diet, an estimated 10% of British children are now obese.

Sports minister Richard Caborn also contributed to the book, financed by the Department for Culture, Media and Sport and published by the Smith Institute, a public policy think-tank.

He said: "We are facing a timebomb in the state of our health. A recent National Audit Office report suggests that obesity costs the UK economy �2 billion each year and the NHS �500m.

"Instances of diabetes in young children have grown alarmingly and promise to store up problems for generations to come. Sport and exercise can help reverse these trends."

"Evidence is beginning to show that schools which have a strong sporting ethos have fewer truants, fewer exclusions and better academic results.

"I see sports projects in my constituency in Sheffield which have helped to keep young people out of trouble with the police. They teach them discipline, teamwork and the valuable lessons of winning with grace and losing with dignity."

The government has set up more than specialist sports schools, with plans to increase this figure to 400.