The government is vetoing the publication of the controversial risk register outlining the full impact of its NHS reforms.
Coalition ministers decided to prevent the release of the register, which assesses the risks and potential casualties of its Health and Social Care Act.
Campaigners had expressed outrage that the legislation became an act of parliament without the government's view of its negative effects being published.
But the Cabinet today decided to block the publication of the risk register for good on the grounds that doing so would undermine the ability of the government to make such assessments realistic in the future.
"Ministers and officials should be able to deliberate sensitive policy formulation, in expectation that their views are not published at a time when it would prejudice the development and delivery of policies," the Department of Health said in a statement this afternoon.
"If such risk registers were regularly disclosed, it is likely their form and content would change, and they would no longer be the effective internal management tools they are intended to be."
Former shadow health secretary John Healey had brought the original freedom of information request forward. The government lost its appeal to the information tribunal in March, before confirming its ruling on April 5th.
"It is totally over the top to place NHS changes on the same footing as preparations for the Iraq war," Mr Healey said.
"There must be some very big risks in the government's NHS reorganisation for ministers to override the law with their political veto."
Health secretary Andrew Lansley insisted he was a "firm believer in great transparency" but said officials needed a "safe space" to discuss difficult issues.
"Had we not taken this decision, it is highly likely that future sensitive risk registers would turn into anodyne documents, and be worded quite differently with civil servants worrying about how they sound to the public rather than giving ministers frank policy advice," he said.
This is only the fourth time that the government has vetoed a freedom of information request in the last decade.
Justice secretary Jack Straw vetoed the publication of the minutes of Cabinet meetings covering the period immediately before the invasion of Iraq in March 2003.
Two further vetoes involved the minutes of a coalition Cabinet sub-committee on devolution to Scotland.