Tessa Jowell, the Public Health Minister, and David Blunkett, the Education Secretary, last year jointly commissioned researchers south of the border to evaluate the health of school-age children. They were particularly critical of PE in schools in England.

Karen McColl, co-author and a researcher at the London School of Hygiene and Tropical Medicine, believed many of the findings would apply in Scotland.

Experts said there was a tendency for PE to focus on competitive sports and team games rather than the individual activities many children like to do and may carry on into their adult lives.

Healthy English Schoolchildren: a new approach to physical activity and food in schools states: “The way PE is taught by some teachers can result in feelings of inadequacy and failure in young people which deter them from further activity. The approach and method of teachers has been shown to influence children’s attitudes to activity. A focus on competitive activities may result in low self-esteem and feelings of incompetence.”

Many pupils failed to identify with their sporty PE teachers. Divisions were reinforced if teachers concentrated on skills rather than promoting a range of physical activities.

Successive Conservative governments promoted the benefits of team games but ministers are now being advised that the priority “should be to promote appropriate activity for all pupils first and only then to promote competitive sports”.

Judy Buttriss, science director at the British Nutrition Foundation, said surveys showed 50 per cent of girls aged 11-16 and 38 per cent of boys did not achieve one 10-minute period equivalent to sustained brisk walking during three school days. There was a “striking fall” in girls’ physical activity after the age of 13.

Mike Lean, head of human nutrition at Glasgow University, said physical inactivity and an excess of calories, particularly fat, led to obesity. Activity burnt up calories. It also improved quality of life, mood, sleeping and cut the likelihood of depression.