British children are among the least active in the world, and fitness levels are plummeting, a damning international study has found.

Experts said the results were alarming, showing that movement was being “stripped out” of modern lifestyles, with children weaned on screen-time and starved of outdoor activity.

On Sunday night Simon Stevens, head of the NHS, called for radical changes in family routines, describing exercise as a “magic pill” which would be a “pharmaceutical blockbuster” if only it could be bottled.