Stormont's top office has been ordered to release the results of a survey it commissioned on the proposed Maze peace centre after a landmark ruling.
Peter Robinson and Martin McGuinness's department acted wrongly in trying to withhold the findings of market research it requested on the controversial project, the Information Commissioner said.
Ulster Unionist leader Mike Nesbitt, whose party successfully challenged OFMDFM's original decision, accused the department of acting like a secret state, adding: "We're not North Korea, we're Northern Ireland."
The Ulster Unionist Party had asked OFMDFM on January 24, 2013 to release the results of the research it commissioned into the proposed peace centre, but the request was refused on the grounds that Mr Robinson and Mr McGuinness were still discussing policy development.
But the Information Commissioner's Office dismissed their argument, describing some of the information currently being kept secret as "innocuous".
Speaking on the eve of his party's spring conference, Mr Nesbitt said there was a systematic lack of transparency in OFMDFM.
"The most telling comment from the Information Commissioner is that OFMDFM failed to make any detailed argument for withholding this information from the public, but rather relied on the argument that they were still in policy development mode as a blanket exemption," he said.
"To me, this is proof of a systemic lack of transparency.
"The ruling also makes clear the Commissioner does not accept OFMDFM's contention that the public would misunderstand the withheld information.
"That was a very patronising argument from Messrs Robinson and McGuinness."
In its ruling, the Information Commissioner's office said OFMDFM had "failed to provide specific and robust arguments" nor an explanation as to why publication "would have an adverse impact on the safe space needed for policy development".
The Belfast Telegraph has regularly reported on the department's poor response rate to FoI requests. Last May we revealed how a request to OFMDFM, which by law should have been answered within 20 days, was outstanding 948 days later.
The query was tabled in September 2010 but, approaching three years on, was still languishing on civil servants' desks.
Mr Nesbitt added: "I consider this ruling a significant victory for the public, who deserve openness and transparency at the heart of government."
How events unfolded:
January 24 2013: The UUP makes an FoI request
February 12 2013: OFMDFM withholds the information.
February 13 2013: The UUP requests an internal review
March 1 2013: OFMDFM upholds its decision.
April 23 2013: The UUP asks the Information Commissioner to investigate.