The liberal Democrat education spokesman has attacked the Government's Pounds 55 billion Building Schools for the Future programme, describing it as a "total mess".
David Laws was reacting to last week's admission by schools minister Jim Knight that it was taking six months longer than originally planned to broker BSF deals.
Responding to a parliamentary question, Mr Knight said the Government had hoped the agreements would be clinched within 78 weeks, but in reality it was taking around 108 weeks.
Mr Laws said: "The Government has made a total mess of this programme. It's incredible that it is taking nearly two years - six months longer than was originally projected - for local authorities to complete the procurement process.
"Nationally, this flagship Government policy is now running two years behind schedule and an estimated Pounds 10 billion over budget. Ministers need to look into why these delays are occurring so that building projects aren't being delayed."
He added: "At a time when the construction industry is crying out for large-scale capital projects, it is unacceptable that this scheme has failed to deliver on its promises."
Last month, The TES revealed that more than a third of BSF schools were finished behind schedule.
But Partnerships for Schools, the agency overseeing the initiative, said it was now ahead of its targets after it changed the "over-optimistic" completion dates.
A PfS spokeswoman said: "The National Audit Office's recent report clearly and unequivocally said that BSF is now being well-managed by Partnerships for Schools and that costs are being kept under control.
"It has been well-documented for the past two years that the original indicative delivery estimates for BSF, set in 2003, were over-optimistic. Having set firm targets back in 200405 - nearly five years ago - BSF is now meeting or exceeding all of these and is on track to have completed or be in the final stages of the last few schools by 2020."
It is understood that PfS will soon take over every aspect of school buildings delivery from the Department for Children, Schools and Families.
The move is believed to be part of a streamlining process taking place across the Government that will hand over delivery to agencies, leaving government departments to focus on policy.