Local authorities have made 213 applications to sell school playing fields since the law was changed in 1998 to protect them - and only six have been refused, it says.
Elsa Davies, director of the charity, said: "If we want to develop the next generation of world champions then we cannot go on selling off these fields."
Figures from Sport England reveal that in 2001-2002 there were 985 applications to build on school playing fields. Of these, 695 were granted.
"Even if schools get new facilities, such as indoor sports halls as a result, it's not much use for a sport like rugby which needs big areas of grass," she said.
Kate Hoey, Labour MP for Vauxhall who was sports minister in 1999-2001, said: "The number of planning applications for development on playing fields has risen every year since 1997, with nearly 1,000 last year. Many of these are for indoor facilities. But the playing field is still lost.
Often there is a double whammy: the land is sold for housing to fund the indoor facility which then gets built on a further tract of the playing field."
Since 1998 schools and authorities have to obtain permission from the Education Secretary to sell off their land and proceeds must go into sports facilities.
The Department for Education and Skills said this has prevented the previous "free-for-all" of playing fields being sold off.
It said that since 1998, the Government has approved the sale of only 133 school sports pitches. Of these, 54 were at schools that had closed. "To say the Government is not protecting playing fields is utter nonsense," said a DfES spokesman. "We are investing more than pound;1 billion to improve sport in all our schools." Of this pound;1bn, pound;459 million will be spent on providing more PE teachers and coaches, staff training and closer links between schools and sports clubs. Another pound;686m is being spent on improving or building sports facilities at 3,000 schools. By 2005 the Government aims to raise the number specialist sports colleges to 400 from the current figure of 231.
WARNING OVER COUCH-POTATO GENERATION
England will not produce more world champions unless radical changes are made to improve school sport.
That is the verdict of Nigel Hook, former head of policy for the Central Council for Physical Recreation. "The state of sport in our schools is poor," he said. "There is not enough time on the curriculum for sport, playing fields are being sold off and many existing ones are very poorly maintained. There are also not enough qualified coaches and teachers who can teach rugby."
Mr Hook said that the rising obesity rate among the young should be a wake-up call to the Government.
"Sport, or rather the lack of it, plays a very important part in people's health," he said.
The Government is committed to ensuring 75 per cent of all children do at least two hours of sport per week in school by 2006. "Some progress is being made but not enough," said Mr Hook.
"I fear that the progress, such as the changes to the curriculum, will take too long. They may be too late to affect the next generation of players."
Margaret Talbot, chief executive of the CCPR, said the sale of school fields made it harder for young people to play rugby. She called for the law to be changed to make it a statutory requirement for councils to be judged on the quality of their sports and recreation facilities.
"There are many authorities who do a lot of good work to maintain fields and open spaces but there are also a lot who do a lot less," she said.