London Playing Fields Foundation has compiled an "at-risk register" of parks threatened by redevelopment. It highlights 20 sites including 5ha Hervey Road in Greenwich, boarded up after several vandal attacks, and the playing fields slated for a new school campus.
The charity said records kept on the state of London playing fields were sketchy and many more sites were likely to be under threat.
Chief executive Alex Welsh added: "The state of our playing fields is not continuously updated and we are losing them by stealth. We need to raise awareness."
London has 16 per cent of the country's population yet only eight per cent of its playing fields, but distribution is as uneven in the capital as across the country."
Kensington has four playing fields and Barnet 97. Tower Hamlets, with 12, has 220,000 people, a third of whom are cricket-loving Bangladeshis, but no grass wicket.
Welsh said old planning guidance had a presumption against developing green spaces. But proposals in the National Planning Policy Framework favoured sustainable development.