School buildings survey to cost a further £6m
An extra £6m will need to be found by a government agency to check the condition of school buildings across England, a funding watchdog warns.
The National Audit Office said the Education Funding Agency had been given "inconsistent data" by local councils.
As a result, the agency faces costs of £6m in unplanned spending to conduct a survey of 8,000 schools - which could divert money from other projects.
Ministers said the surveys would ensure fair allocation of maintenance funding.
The Education Funding Agency (EFA) was set up by the Department for Education in April 2012 in an attempt to improve efficiency, accountability and transparency in the education sector.
It is responsible for making sure school funding agreements are in place, providing funding to schools and colleges and overseeing the maintenance and construction of their buildings.
The government gave the EFA responsibility for the property data survey programme, which set out to collect data on the condition of approximately 23,000 schools in England by October 2013.
The findings were to be used to help make decisions about which schools should be refurbished or rebuilt.
To complete the programme, the EFA commissioned surveys of 57% of schools and relied on local authority data for the rest.
But a month before the programme was due to be finished, the EFA identified "inconsistencies in the data supplied by local authorities".
As a result, Education Secretary Michael Gove announced in November that the Department for Education (DfE) was commissioning surveys of the 8,000 schools that were meant to be covered by the council information.
"This will cost the agency £6m in unplanned spending, potentially diverting resources from other projects," the NAO report said.
"The delay in collection means that the data will not be available as planned to inform capital maintenance funding allocations in December 2014.
"This suggests that the agency may have been over-optimistic in its planning assumptions around the consistency of local authority data."
A spokesman for the DfE said: "It has always been the intention to complete school surveys on the new consistent basis, over time. So this brings forward the expenditure of £6 million from future years.
"The benefit will be a consistent database that will be used to allocate maintenance funding to get the best return from the government's investment in the school estate."
The NAO also reported that the EFA had fulfilled most of its responsibilities, but warned that it could be at risk of being "overloaded" amid a growing demand for its services and increasing expectations by the DfE.
Amyas Morse, head of the National Audit Office, said: "Given the agency's expanding remit and rapidly growing customer base, it must now bring together its existing improvement plans and quickly implement an operating model capable of dealing with the new demands.
"Our experience of similar bodies in other sectors suggests that the agency might otherwise become overloaded, to the detriment of its own performance and risking value for money across the education system."
Margaret Hodge, chair of the Commons Public Accounts Committee, said: "The department [DfE] needs to make sure that it clearly understands the delivery capability of the agency so that it is clear about what it expects the agency to achieve.
"I fail to see how the agency can reduce costs by 15% whilst simultaneously expecting to see a 50% increase in demand for its services.
"There is a real danger that the agency will simply become overloaded, putting at risk the value for money it achieves from its £51bn of funding."