Senior police officers may have "influenced decisions" regarding the investigation into the late Lord Janner over child abuse allegations, a report has found.
The Independent Office of Police Conduct (IOPC) has said it had found evidence suggesting Leicestershire Police failed to properly investigate accusations against him.
The force led three investigations into the Labour peer and former MP in 1991, 2000 and 2006. None led to any charges against him.
Lord Janner died in December 2015 having been deemed unfit to stand trial over 22 counts of child sexual abuse. His family has repeatedly protested his innocence.
The IOPC has produced a report updating the Independent Inquiry into Child Sexual Abuse on its investigation which it launched in 2014 in response to a Times article that alleged a detective had been "ordered to limit his inquiries into Greville Janner".
The preliminary IOPC report said of the 1991 investigation: "Based on the evidence reviewed by the investigation, there is an indication that senior officers may have influenced decisions regarding the enquiries being carried out."
It added: "Specifically, and again based on the evidence reviewed by the investigation, there is an indication that police documents may have been inappropriately modified."
The IOPC report notes the probe in the early 1990s followed "a number of references to a relationship, including a sexual relationship, between Lord Janner and a child". But the police watchdog could not find any evidence these claims were looked into.
In the early 2000s, there were "allegations made by former children's home residents" which "appear from the evidence available not to have been investigated or recorded", the IOPC added.
It also noted "documented results of investigative actions regarding Lord Janner [that] appear to contain information that could be interpreted as misleading and/or inaccurate".
Lord Janner's son Daniel Janner QC reacted to the IOPC report, saying: This private document should never have been published.
"It is yet another astonishing example of this discredited inquiry's mishandling of information."
He said the inquiry's investigation into his father was "macabre proxy prosecution of a dead innocent man who cannot answer back from the grave".
