Politicians have been accused of paying "lip service" to sport while high numbers of inactive youngsters threaten to put strain on the health service.
Tim Lamb, chief executive of the Sport and Recreation Alliance, wants a major rethink on sports strategy.
"I think there's a lot of inspiration, a lot of warm words, but we need to see that translated into action," he told BBC Sport's Dan Roan.
He spoke out as Sport England announced a £493m investment in grassroots sport.
"There's a lot of good things going on but the Sport and Recreation Alliance believes a lot more needs to be done," he said.
The government has said it is putting competitive sport at the heart of the new national curriculum and spending £1bn on youth sport over the next five years.
But the Alliance, an umbrella group for sport's governing and representative bodies in the UK, believes the government is not treating the issue as seriously as it should.
"There are some really scary statistics around," said Lamb, a former professional cricketer and chief executive of the England and Wales Cricket Board.
"Something like 30% of all children leaving primary school to go to secondary school are either clinically obese or overweight and that's storing up massive problems for the health service for years to come," said Lamb.
"We spend something like £33bn a year treating disease which is entirely preventable if people took enough physical exercise or played sport.
"It's been calculated that unless we do something about the obesity problem it could threaten the very existence of the health service in 20 or 30 years' time.
"The key problem is politicians don't look far enough ahead. Their priority is to get re-elected in however many years' time.
"This is the time for parties to put petty politics aside and really draw up a proper strategy.
"There's never been a better time to capitalise on the opportunity of the Olympics and Paralympics and if we don't take the opportunity now it will be a chance wasted."
"I'd like to see better training of teachers for teaching PE - a qualified PE teacher in every school. I know that's a big ask but the stakes are very high.
"The question of sport and physical activity in our schools needs to be taken more seriously. There needs to be a complete re-look at the whole strategy and much more investment and much more emphasis on school sport in future."
Lamb said sport was a force for social good, leading to more active and healthy lives, helping academic attainment, reducing anti-social behaviour and even building community cohesion.
But he added: "Sport can do all these things and I've never felt that government has taken the issue seriously enough. They pay lip service to the importance of sport, but more needs to be done at cabinet level, at cross-party level if we're to tackle some of the problems we're facing in this country."
Lamb suggested cutting red tape could help clubs and associations.
"The government is talking a good game about it but the average community sports club has to acquire something like 33 licenses just to operate," he said.
"We need to reduce bureaucracy, we need to make the life of clubs, officials and participants that much more straightforward, much more uncomplicated and take the whole question of community sport much more seriously."