The Department of Health has lost an appeal against publishing a risk assessment of its NHS reforms.
The department appealed against a ruling, given in favour of a Freedom of Information request by Labour MP John Healey, arguing that it was exempted from releasing information used in policy formulation.
The information rights tribunal upheld the original decison by the information commissioner that the risk document, compiled in November 2010, should be made public.
The coalition government has been wary of publishing the document, which will analyse the possible risks in the controversial shake-up of the NHS proposed by health secretary Andrew Lansley.
Healey told the Guardian after the appeal: "The judgment backs the public's right to know about the risks the government is taking with its NHS plans."
A DoH spokesman said: "We are awating the detailed reasoning behind this decision. Once we have been able to examine the judgment we will work with colleagues across government and decide the next steps."
The government can still appeal to an upper tribunal to block publication.
During the two-day tribunal hearing, Una O'Brien, a senior health civil servant, argued that the information would have an "insidious" effect as the risk register was supposed to represent a "safe space" where advisers could discuss plans frankly.
Labour and the coalition have clashed repeatedly over releasing the report. Prime Minister David Cameron turned the tables on the opposition by claiming that shadow health secretary Andy Burnham had blocked the publishing of a register in 2009.
Burnham praised the tribunal decision on Twitter, saying: "What a breakthrough in fight to save NHS from risks of reorganisation. Huge credit to John Healey. PM must accept ruling with good grace."