All police forces in the country will be made to examine their archives to search for evidence of misconduct by undercover officers following allegations surrounding the Stephen Lawrence murder inquiry.
Policing minister Damian Green admitted the probe could lead to "some very unpalatable truths" coming out, but said it was better than keeping them hidden.
He is expected to tell the chief constables of the 43 forces in England and Wales they must carry out the searches following the revelation that an undercover officer was told to find information to use to smear the Lawrence family after the teenager's racially aggravated murder in 1993.
"Nobody who cares about the police wants to have a constant stream of historic scandals coming out," he told the Sunday Telegraph.
"That is why we are asking every chief constable to look at what may have happened in the past, and to do so as soon as possible. We may discover some very unpalatable truths, but it is better to discover them now than leave them hidden.
"What was clearly going on for too long was an inward-looking culture where police officers believed what they wanted to believe."
Mr Green is also expected to announce that the new College of Policing is drawing up a code of ethics for officers, the paper said.
"We will take steps to ensure the police are transparent," Mr Green told Sky News.
"To make sure that there are is a proposed code of ethics that everybody knows about so we can carry out changes in culture."
It has emerged that a retired senior Scotland Yard police officer admitted authorising secret recordings of a meeting between Mr Lawrence's friend Duwayne Brooks, his lawyers and detectives. Ex-deputy assistant commissioner John Grieve said police officers had wanted "an unassailable record of what transpired" in meetings in 1999 and 2000.