British prime minister Margaret Thatcher was told “drunken Liverpool fans” were to blame for the Hillsborough disaster, according to government documents leaked to the BBC on Thursday.

The official inquiry ruled that the disaster, in which 96 people died at an FA Cup semi-final in 1989, was caused by a failure in crowd control by South Yorkshire police.

Documents that had remained secret are being reviewed by the Hillsborough Independent Panel, set up in 2009, but were not scheduled to be released to the public until the autumn.

The leaked documents include a letter sent to Thatcher by a member of her policy unit in Downing Street four days after the disaster.

It contains a version of events described by the chief constable of Merseyside police, the late Sir Kenneth Oxford, and some of his senior colleagues in the immediate aftermath.

The letter claims that Oxford said that “a key factor in causing the disaster was the fact that large numbers of Liverpool fans had turned up without tickets. This was getting lost sight of in attempts to blame the police, the football authorities, etc.”

It went on to report that an unnamed senior member of the Merseyside police directly blamed supporters: “One officer, born and bred in Liverpool, said that he was deeply ashamed to say that it was drunken Liverpool fans who had caused this disaster, just as they had caused the deaths at Heysel.”

The nature of the leak has already caused concern.

“We are really concerned that the emphasis is totally on Merseyside police here and not on South Yorkshire police, and that makes us very suspicious of how this information was leaked,” said Sheila Coleman of the Hillsborough Justice Campaign.

“We find it a strange coincidence that this information was leaked only days after we found out the (Hillsborough Independent) panel are not going to report until the autumn.”