The Cabinet Office has been accused of attempting to cover up information about Whitehall's knowledge of Cyril Smith's child abuse at the time he was granted a knighthood.
The documents revealed that Margaret Thatcher was made aware of allegations involving the Liberal MP before he was given the honour.
The papers, released to the Mail of Sunday following repeated demands for disclosure, also show that the country's most senior civil servant wrote to the director of public prosecutions to find out why Smith did not face justice for alleged offences against teenage boys.
The newspaper first requested the documents under the Freedom of Information Act in April last year but they were only released on Friday following an intervention by the Information Commissioner.
The 19-page dossier of information on the decision to confer a knighthood on former
Rochdale MP Smith in 1988 included one undated letter, marked secret, from a member of the Political Honours Scrutiny Committee to Mrs Thatcher, warning of "the risk that such an award could give rise to adverse criticism".