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.

Paul Burstow, health spokesman, said: "To create a healthy Britain in the long-term, action must be taken now to tackle cases of overweight children.

"The government must stop sending conflicting messages in the fight against obesity. By backing initiatives like the Cadbury's 'eat chocolate to get fit' campaign, the government is undermining efforts to change behaviour.

"Health promotion has fallen off the government's agenda. It is time Ministers sent a consistent message about the benefit of good diet and exercise."

Forum Response: British Retail Consortium

Bill Moyes, director general of the BRC, told ePolitix.com: "Food retailers have been heartened by reports that the government is considering the most appropriate way of encouraging increased levels of physical activity as part of its policy of improving the nation's health.

"That exercise, along with diet and the management of stress, plays a central role in our health is unquestionable.

"The sector has wholeheartedly endorsed the government's key message that eating a balanced and varied diet is an important component for a healthy lifestyle.

"Food retailers have been at the forefront of helping their customers overcome the factors that are perceived to act as barriers to healthy eating by investing heavily in new product development, introducing nutrition labelling and pioneering consumer communication strategies.

"The challenge now for the government is to educate and support consumers in choosing better diets as part of healthier lifestyles through a concerted public information campaign that provides clear, simple, consistent and scientifically credible messages."

Forum Response: Royal Yachting Association

John Derbyshire, racing manager and performance director at the RYA, told ePolitix.com: "If the government is series what they need to do is recognise three things; Sport for Sports sake, sport for health and sport for education.

"The sport for sports sake should come out of sports council money.

"A proportion of the money that goes to the department of health the government should allocate to sport for health sake and money from the department of education should be provided to educate people in the benefits of sport."