Gold medallist accuses Olympic planners of not looking ahead and will urge ex-champions to help save children from obesity

The record-breaking Olympian, who won five consecutive gold medals for rowing, says those involved in the Games are not looking far enough into the future. "Everything seems to be very short-term at the moment – there has been little talk about what is going to happen in the years after the Olympics. The success of these games will not even be what happens in 2013, but what happens in 2020 and beyond,"he told the Observer.

Redgrave, who is advising the government on how to get more people taking part in sport in his role as "2012 sports champion", also warned that the country had reached a tipping point, with too many children and adults leading sedentary lives.

"We are very much on a brink – if you look across to America, obesity rates are sky-high," said Redgrave. "In some parts of the US if you can't drive somewhere, you don't go." He warned that Britons also had to be aware of a general lack of activity. "There are scary statistics that suggest our children might die at a younger age than we will – that life expectancy will start to fall."

Redgrave described how as a child he would ride his bike, play football and climb trees all around his Buckinghamshire home, less than an hour's drive from London. "It is more commuter belt now, and there is not the same freedom. Society has changed. We used to walk to school, but now most of the kids get dropped off and picked up." The former rower said part of the problem was safety concerns.

Redgrave is helping to draw up a document that will advise ministers on what must be done to ensure a sporting legacy from the games. He is expected to call for former sports stars to come out of retirement to help inspire children and adults. He will also propose a mass participation scheme in a wide range of sports using clubs around the company.

A spokeswoman for the Department for Culture, Media and Sport said the only way to turn the tide on obesity was for government, families and industry to work together. She said school and youth sport had never been so well funded, with £2bn of ring-fenced investment between 2003 and 2011.

"All children should have the opportunity to play sport, no matter what their background or ability. Today 90% of pupils are doing two hours of PE and sport per week in schools, but we want to go even further. In the run-up to 2012, our focus now is on the challenging ambition of getting young people to take up the offer of five hours of sport a week, in and out of school time." She also highlighted a major play strategy that aimed to get children having fun with friends instead of sitting indoors.

Margaret Morrissey, founder of the website Parents Outloud, said part of the problem was that there was too little space for children to play and complained of youth centres closing down in her region. "They are building smaller houses with minute gardens," she said. "So children don't have anywhere safe to go."