Concerns are mounting about schools encroaching on green spaces as the growing primary-age population puts pressure on councils to develop classrooms on open land.
In a recent case, an Upper Tribunal court judge decided that he would only rule on private rather than public interests related to an 1893 covenant between landowner John Innes and Merton Council's predecessors to protect Dundonald Recreation Ground from a school expansion.
Parks consultant Dr Sid Sullivan said: "I've seen too many parks turned over to schools and we never get the ground back. We can't afford to lose green space and we're not likely to get the public to buy into it."
The expansion of Dundonald Primary School onto adjacent park play areas, tennis courts, a pavilion and bowling green to double its entry numbers could get underway in November.
Meanwhile, Lewisham Council is investigating temporary classrooms in Home Park while building work takes place to expand Adamsrill Primary School.
Councils have been criticised for not planning ahead over school places. Last week MPs blamed the situation on the Department of Education.
Sullivan said temporary classrooms are "a great idea" but he would only support them if the classrooms could be set aside for community use in the evenings and at weekends.
He added: "The people who are going to invest in our parks are the younger people. If they have (temporary) lessons in the park they are likely to appreciate parks."
Provision of sufficient school places is a statutory responsibility for local authorities while parks provision is not.
Pressure on classes
The number of children in infant classes of more than 30 has more than doubled over the past five years and 20 per cent of primary schools were full or over capacity in May 2012.