Before and after: just one of the 1,250 playing fields that have vanished beneath concrete

They are the lungs of the inner cities and the focal point of village life. But a report revealing the mass transformation of Britain's playing fields into building sites and housing estates yesterday prompted warnings for the health of future generations.

Ministers are urgently preparing measures to stop further sales of playing fields, as it emerged that more than 1,250 sites have been sold or offered to developers for housing and other building projects.

An unpublished report by the Central Council for Physical Recreation reveals the extent to which schools, local authorities, health trusts, railways and private companies have raised cash by selling off their sports grounds.

The report reveals that in the last 12 years, 1,272 playing fields have been developed or face development. A staggering 251 sites have been proposed for sale in the last eight months since a requirement to consult the Sports Council about prospective sales was introduced.

David Blunkett, the Secretary of State for Education, and Chris Smith, Secretary of State for National Heritage, are preparing measures to reverse the trend "as a matter of urgency".

Restrictions will probably be introduced to make further sales of sports fields possible only when there is no local support for their retention. Nigel Hook, technical services director of the CCPR, said many primary school playing fields of less than one acre had been sold without notification and were not included in the figures. "It's a disgrace. The legislation encourages local authorities to sell off playing fields which could be used by young people. No wonder youth sports development is withering on the vine," he said.

The Labour peer Lord Dormand of Easington has been lobbying government ministers to do something to stop the sell-off.

"It is absolutely scandalous," he said. "The practice of selling off the playing fields has not just been promoted but actively encouraged by the previous government." He said new legislation was needed to ensure sales could not go ahead without government approval. "If it is left to the local authorities, some of them would be more interested in the money."

Among the sites threatened by developers is the former sports field of the Foster's Boys Grammar School in Sherbourne, Dorset. Plans by Dorset County Council to turn the nine-acre site into an estate of 107 homes have infuriated local people.

Doug Hoskins, leader of the "Fight for Foster's Field" campaign, said it was the only green site left in the town for informal recreation. "We want it to be like an old-style park for everybody from eight to eighty," he said. "In the last 18 months, 52 houses have been given planning permission around the perimeter of the field. They are crowding in houses everywhere they can."

In Shropshire, campaigners are angry at plans by the West Midlands Regional Health Authority to build houses on land alongside the Royal Shrewsbury hospital which was once a sports field for hospital employees.

The rush to sell off playing fields began with the Department of Education's Circular 909 introduced in 1981. Despite a succession of promises by ministers to reverse the trend, the sales have continued.

Don Earley, deputy director of the National Playing Fields Association, called for new laws to give sports grounds the same protection from development given to green belt land "In fitness terms, you end up as a less healthy nation," he said, "and Britain will have less chance of producing outstanding performers."