The Conservatives have signalled that they will pull the plug on planned school building projects if they form the next government.
Shadow schools minister Nick Gibb has admitted that only schools that have reached "financial close" with a preferred bidder will see their projects completed.
The decision could result in millions of pounds of wasted public money as local authorities and schools invest heavily both financially and in man hours to prepare for the Building Schools for the Future programme.
Mr Gibb, speaking at a seminar two weeks ago, said decisions on whether schools will be rebuilt or refurbished under BSF will be made on a "case by case" basis, according to Education Investor magazine. He said: "What we're saying is that if financial close has been reached, it will go ahead... (If not) then it won't be guaranteed."
However, he stressed that building projects would not be cancelled across the board. "Shadow ministers are told on pain of death not to make spending promises," he said.
Mr Gibb said: "We think (BSF) is a hugely wasteful approach to procuring new buildings. It's very top down, very bureaucratic and costs a huge amount of money."
The party also hopes to divert significant amounts of money from the capital investment programme to fund the surplus places it needs to kickstart its free school movement. But the decision to cut certain school building projects could see millions of pounds in fees being wasted, creating a legal backlash from contractors.
Earlier this week, Schools Secretary Ed Balls announced that a further six local authorities had entered the BSF programme.
In response to Conservative plans, Mr Balls said: "We already knew the Tories were planning to cut our school rebuilding programme by #163;4.5 billion in areas which have not yet joined the BSF programme.
"But the shadow schools minister's admission that all areas where final contracts have not yet been signed and sealed could also see building projects cancelled means hundreds more schools than we previously thought are at risk from the Tories." He added: "Teachers, parents and young people in all these areas will now know that a Tory axe hangs over their new school building."
Ty Goddard, chief executive of the British Council of School Environments and founder of think tank Centre for School Design, said the admission marked the start of the battle over school capital investment.
Mr Goddard said: "Everyone knows that it will be a vote-deciding issue in marginal seats at the general election.
"For us, the choice is stark - no-one wants a return to leaky roofs and unsafe schools, nor do they want money wasted on the bureaucracy that has haunted the BSF programme."