The Gateshead Millenium Cohort study tracked more than 500 children for eight years, with trackers measuring activity levels.

Until now, efforts to improve uptake of sport and fitness have assumed that the significant slump in activity comes with puberty, especially with girls.

But the new study shows a sharp drop in activity levels between the ages of seven and nine, among boys and girls, with a decline continuing into adolescence.

At the age of seven, the average boy was moderately or vigorously active for one hour 15 minutes a day, the study found, dropping to one hour 10 minutes by the age of nine, and just an hour by the age of 12. By the age of 15, the figure is just 51 minutes, the research shows.

Seven-year-old girls had such activity levels for 63 minutes a day, dropping to 56 minutes by the age of nine, and 47 minutes by the age of 12. At 15, the average girl is active for just 41 minutes daily, the tracking devices found.