David Hart, General Secretary of the National Association of Head Teachers, said that a survey of PE and sports in state schools showed that children were in danger of becoming a "generation of couch potatoes".

"Nothing illustrates the yawning gap between the affluent independent sector and the strapped-for-cash state sector quite so starkly as the state of PE and sports facilities," said Mr Hart.

This decline in school sports would have consequences for the future health of the nation, said Mr Hart. "The fitness levels of a significant number of youngsters, and their sedentary lifestyle, are already a grave cause for concern."

Few primary schools have gyms, swimming pools or tennis courts

As well as a lack of facilities, schools surveyed complained that pressures on raising academic standards have pushed PE and sport to the margins. In response, the NAHT is calling for more protected space in the curriculum for sport.

The survey of over 2,000 schools concluded that "primary school facilities are woefully inadequate" and that "little if any money" has been received from the National Lottery for school sport.

According to the survey, 51% of primary schools do not have their own playing fields, 28% of secondary schools have poor drainage on playing fields.

It also says that 94% of primary schools have no gym, 92% have no swimming pool and 97% have no tennis court - although it is perhaps more surprising that some do have these facilities.

The survey highlights particular problems with swimming lessons, which the NAHT says depends on the financial support of parents in a "worryingly large" number of schools.

In response, the NAHT is calling on the government to recognise the importance of school sport and to fund it accordingly.