The chance to build an Olympic legacy of wider participation in sport has been "squandered", according to Dame Tessa Jowell.
The former Olympics minister, part of the team that helped secure the 2012 Olympic and Paralympic Games for London, branded the coalition government "wicked and negligent".
While the regeneration of east London had been a success, cuts to school sports programmes had left grass-roots participation "back where we started in 2002", the London mayoral candidate said.
Dame Tessa told the Guardian: "Instead of a generation of children being transformed by sport, a generation of children have been robbed of the chance to discover a sport they're really good at.
"We were on track. It was absolutely, wholly and solely their fault. It was going to be delivered. We were on course to deliver it as the figures make absolutely clear. Whenever I think about it, it makes me furious that this opportunity was squandered. My fury is on behalf of all those who were starting secondary schools five years ago.
"I hope this is a huge stain on their consciences. When we get to Tokyo (in 2020) I think it likely we'll be back to half our medallists being from independent schools. It doesn't mean they're great athletes.
"There are fewer people now playing sport. It is on the conscience of those ministers."
Sport England's latest figures from April 2015 suggested the number of people over 16 participating in sport at least once a week stood at 15.49 million, down from 15.89 million in October 2012.
A total of 1.4 million more people have been playing sport since the first year of Sport England's Active People Survey 2005/06, when the Olympics were secured.
Last month Boris Johnson defended the Government's record in the Commons, saying all major venues had been or were set to be opened to the public and the private investment in London which followed the games had ensured "a phenomenal legacy".