An official inquiry is launched today into the sale of unhealthy foods to children amid alarming evidence that Britain is facing an obesity "timebomb".

The investigation by the Food Standards Agency (FSA) could lead to a ban or tough restrictions on promoting fattening, salty and sugary products on television and in stores. Using popular cartoon or TV characters to promote unhealthy foods could also be banned.

The proposals, which have alarmed the advertising industry and food manufacturers, come after a series of official reports that have revealed child obesity is reaching epidemic levels in Britain.

Reports by the FSA and the National Audit Office, Parliament's spending watchdog, disclosed that nearly 10 per cent of six-year-olds and 15 per cent of 15-year-olds are obese. The average child eats just two portions of fruit or vegetables a day. According to the NAO, a quarter of British adults could be clinically obese by 2010, largely due to the poor diets and unhealthy foods eaten by today's teenagers.

Yesterday, the Department for Culture, Media and Sport indicated it was already nervous about the impact of the review on the advertising industry. In a statement, it welcomed the study but insisted food promotion was only part of the issue.

"There's more than one way to skin a cat ... that's why we're spending £459m on school sports over the next three years," the statement said.

However, Sir John Krebs, the FSA chairman, warned that the agency would recommend tough action on dangerous advertising. "We already know many children's diets contain more fat, sugar and salt than is recommended," he said. "We know the level of obesity in children is rising and, in the words of the Chief Medical Officer, is a health timebomb that could explode.

"By 2010 it could cost £3.6bn a year and be a very significant factor in the ill health of thousands of people. Doing nothing is not an option."

Last week, the Consumers' Association alleged major food manufacturers were targeting children with breakfast cereals, ready meals and tinned foods that exceeded health limits on salt, fat and sugar. Some packets claimed the food was "healthy".