The schools Secretary, Ed Balls, has blocked a Tory freedom of information request demanding publication of a report on potential cash-savings in education spending because it would interfere with his ministers' "thinking space".
The Conservatives had written to civil servants calling for the Department for Children, Schools and Families to publish the recommendations of the Handover Report after it was leaked to the BBC.
Last November, Mr Balls announced that he had turned to former WH Smith chief executive Richard Handover to investigate areas where his department could provide better value for money.
But Mr Balls was forced to distance himself from the findings after a BBC story claimed that millions were being wasted.
Mr Handover is believed to have said headteachers appear not to understand the concept of value for money and to have recommended cutting 40,000 teaching assistant jobs.
The study points to a primary school that spent #163;50,000 installing three toilets (five times the proposed sum), and one that spent #163;35,000 on a photocopier worth just #163;1,000.
Tory party workers submitted an FoI request only for it to be rejected last week to protect ministers' "thinking space". They are planning to appeal to the Information Commissioner.
A letter from the DCSF stated: "Good government depends on good decision-making and this needs to be based on the best advice available and a full consideration of the options.
"Without protecting the thinking space and the ability for ministers and senior officials to receive free and frank advice, there is likely to be a corrosive effect on the conduct of good government, with a risk that decision-making will become poorer and will be recorded inadequately.
"In this case, it is the department's view that the public interest in non-disclosure outweighs the public interest in disclosure."
The Tories have described the move as "unbelievable", adding that Mr Balls is refusing to publish the report in a bid to spare its blushes.
Michael Gove, the shadow schools secretary, said: "It's unbelievable Ed Balls is blocking the publication of this vital report so he and his other ministers can have their 'thinking space'. Given the commission of the report was highly publicised, it seems he is now trying to suppress it to avoid more embarrassing details of his chaotic running of the department becoming public."
Mr Gove added: "Handover said the department has little clue about financial efficiency and that millions of pounds are being wasted on poor spending decisions. But it's impossible for politicians to make judgments about how money can be saved in future if the Government refuses to publish studies like this into what is going wrong."
A DCSF spokesperson said: "The nature of the study meant Mr Handover necessarily made broad assumptions and extrapolations based on limited evidence and specific examples. Publishing the withheld information would pre-empt further work and - given the provisional nature of his findings - risk undermining the process going forward. This is not in the public interest."