Sutton is facing a shortage of 400 secondary school places after it emerged that £280m of planned funding is under threat.
The new coalition government is expected to freeze the national Building Schools for the Future (BSF) programme pending a spending review.
Sutton Council said that without the funding the borough will face a shortage of around 400 secondary school places by the end of the decade.
In the first stage of the programme, the council had planned to spend £65m developing five schools in the borough.
Wandle Valley, The Limes College, Carshalton Boys Sports College, Carshalton High School and the Hospital and Tuition Service were all due to be rebuilt or expanded.
The council said, with its secondary schools already oversubscribed, it needs about 13 extra classes at each year over the next 10 years.
But there are fears that authorities who have not already named their contractors may lose funding. This would mean that only the more advanced development at Stanley Park High School would be safe.
In February, Conservative MP Michael Gove, now Education Secretary, said he would carry out a full review of the BSF programme.
He said he would try and honour existing projects but could not guarantee any additional money for further improvements.
Councillor Ruth Dombey said: “Though we know the huge national budget deficit means government has to cut its spending, it would be wholly unfair to local children to withdraw BSF funding to councils like Sutton at a late stage”
She also said, after significant pre election pressure and clear and unambiguous assurances that the project would go ahead, the council had spent money preparing its application. As a result, the council is now asking for a guarantee of the funding or for the council to be refunded the money it has already spent.
Vivien Jones, head teacher of Carshalton High School for Girls, said: “The BSF programme is not just about buildings, it’s about transforming learning. “We have still got a lot of mobile accomodation and one of them is in a particularly bad state of repair. "They are not conducive to 21st century learning and would have all gone if we received the funding.
“We have had great results over the last few years and have worked hard to do that. If we had these funds we could look to branch out and be more innovative in motivating students and add another dimension to the learning experience.”
A spokesman from the Department for Education, said: “We have not yet announced anything but the department’s spending will be reviewed in due course.”