Academies face being forced to sign land over to the government so that new schools can be built to tackle the growing pupil places crisis, TES can reveal.

Changes to funding agreements mean the Department for Education now has the power to compel academies to give up parts of their grounds, as schools struggle to cope with the increase in pupil numbers.

The prospect is likely to be a major concern for academy headteachers across London, the South East and other big cities, where pressure on places is reaching a “tipping point”, according to the Local Government Association. Nationally, an extra 450,000 new places are needed over the next five years, with approximately 900,000 needed in the next decade.

Lawyers said the DfE had ushered in the changes “almost through the back door” by altering the funding agreements of all new academies. But the department, which has put pound;7.35 billion of funding into creating more school places, said the move was necessary to ensure “the best use of public land”.

“This change to academies’ funding enables us to work with new academies with surplus land to explore ways of using it to meet demand for places in the area,” a spokesman said.

As TES reported last year, about one in three primary schools have built classrooms on their playgrounds to meet growing demand for places.

Malcolm Trobe, deputy general secretary of the Association of School and College Leaders, said the new DfE powers would worry some headteachers, but added that the need for more schools was clear.

“It will be a worry for heads, particularly in areas such as London, but we have to be sensitive to the national and local demand that there is for additional school places,” he added. “Obviously schools will not want to lose their land - they will wish to use their buildings and playing fields for their own purposes. But where there is demand for extra places we have to look at ways of using the land.”

Mr Trobe said the issue of whether schools that gave up their grounds should receive “financial recompense” was a grey area.

The government has been criticised for not responding quickly enough to the squeeze on school places and for relying too heavily on the free-school programme to meet the demand for extra places. Ministers decreed that any new school must be an academy or free school “in the first instance”, but the free-school programme has been hamstrung by a lack of viable sites, particularly in the capital.

Natalie Evans, director of the New Schools Network, a charity that helps groups to open free schools, said any move to address the “acute shortage” of places was welcome.

“We know that finding sites remains the single biggest challenge facing new schools, so the government needs to be creative in its response,” she said. “Free schools are an example of what can be done. They have opened in unconventional buildings that are refurbished and on under-utilised land.”

Russell Hobby, general secretary of the NAHT headteachers’ union, said he understood why the change had been made but described it as “quite a backtrack” for academy freedoms.

“Heads convert their schools to academies to be masters of their own destiny and they are now facing serious interference,” he said. “Land in particular has always been a touchy subject for academies.

“It also shows the real weakness of having to rely on funding agreements to manage stress in the system. Funding agreements are fragmented, they are less open to scrutiny and they are easy to change without much consultation.”

The changes are outlined in model funding agreements published by the DfE. Where the Education Funding Agency has provided school sites, academy trusts “must share occupation of the land” with other academies deemed appropriate by the education secretary. Where land is leased to academies by a local authority, the education secretary will consult on whether the ground could be “sublet” by another school.

The reform will affect only new academies to begin with. But Alison Talbot, a partner at law firm Blake Morgan, said it would impact on a growing number of schools. If any existing academy applied for a capital grant or took on another school they would be required to adopt the new funding agreement, she said, leaving them subject to the land-sharing rules.

“It came into the new funding agreement almost through the back door,” Ms Talbot added. “The DfE is the ultimate regulator and controller of funding.It is likely that the moral and political pressure on a school will be fairly intense if they try to resist a land-share arrangement.”

David Simmonds, chair of the Local Government Association’s Children and Young People Board, said the school places crisis was approaching a “tipping point”, particularly in big cities. “We have expanded all the existing schools as much as we can, but now we need to open new ones if we are to address the shortage of places,” he added. “So to have this written down in academy agreements is very welcome.”