A leaked letter has revealed that the prime minister believes a more "interventionist" approach is needed to improve national fitness levels.

Tony Blair, who plays tennis and goes to the gym four times a week, says in a letter to culture secretary Tessa Jowell that he wants to use London's bid for the Olympic Games as a catalyst to counter lethargy among adults and children.

Downing Street believes that increased sporting activity is vital to reduce rising levels of obesity in the young and prevent massive future health bills for diabetes and heart disease.