The government has been ordered to release cabinet records of discussions in the immediate aftermath of the 1989 Hillsborough stadium disaster.
Prime Minister Margaret Thatcher was briefed about the tragedy and held several meetings about the disaster in which 96 Liverpool fans died.
Information Commissioner Christopher Graham ruled that the information was in the public interest.
The Cabinet Office said it had yet to receive the commissioner's ruling.
Mr Graham's judgement relates to a Freedom Of Information (FoI) request from the BBC which was refused by the Cabinet Office in 2009.
The government has either 28 days to appeal or 35 days in which to release the documents.
The secret files include reports presented to Mrs Thatcher and correspondence between her office and the then home secretary Douglas Hurd, and minutes of meetings she attended.
Mr Graham's decision notice said the "specific content of the information in question would add to public knowledge and understanding about the reaction of various parties to that event, including the government of the day, in the early aftermath".
Mr Graham also criticised the Cabinet Office for "unjustified and excessive delays" in handling the BBC request.
The request had been followed by an internal review which upheld the refusal.
Relatives of the Liverpool fans who died in the Hillsborough tragedy said they were pleased they might discover Mrs Thatcher's thoughts on the disaster.
They expressed surprise that the commissioner had ordered the Cabinet Office to release the documents, despite the 30-year rule stopping publication of cabinet minutes.
Pat Joynes, a member of the Hillsborough Family Support Group, said: "I'm very pleased that the papers are going to be handed over.
"Twenty-two years ago, when Mrs Thatcher came to Liverpool Cathedral, my husband asked her face to face if there was going to be a cover-up, and she said: 'Mr Joynes, there will be no cover-up.'
"But there has been a cover-up which has persisted ever since."
Another member of the group Anne Williams, who lost her 15-year-old son Kevin in the tragedy, said: "This is good news. I'm very surprised.
"I thought the government would block it. At least now, we may get to the truth."
Ninety-five Liverpool supporters were killed in a crush of fans at the Hillsborough stadium in Sheffield, where the club was playing an FA Cup semi-final against Nottingham Forest.
The 96th victim was left in a coma for three years and died in 1992.
An inquiry into the disaster held that the main reason for the overcrowding was the failure of police control.
Correction 27 July 2011: An earlier version of this report contained an image which was not appropriate. We apologise for this error and any distress it may have caused.