Scotland Yard has defended its handling of the Lord Brittan abuse allegations but accepted his widow should have been informed sooner that he would face no action over the rape claim.
The Metropolitan Police said criticism of its handling of previous allegations against public figures influenced its actions in the Lord Brittan case and led to a delay in the case being resolved.
Lord Brittan died in January without being told he had been cleared of the allegation.
The Met held an internal review after writing to Lady Brittan earlier this month to apologise for failing to inform the family her late husband had no case to answer.
The report, which saw the Met publicly name former home secretary Lord Brittan in relation to the case for the first time, outlined a timetable of the case ahead of a Commons Select Committee hearing next Wednesday.
The lengthy statement, issued amid a continuing furore over the allegations raised by Labour deputy leader Tom Watson, also confirmed a separate force will review the Met's handling of the investigation.
Investigating officers told the person who made the allegation in April that there would not have been a prosecution had Lord Brittan been alive, but his legal team were not told at the same time.
The Met concluded "Lord Brittan’s solicitors should have been informed" no action was to be taken against the late peer at the same time as the complainant was informed.
"This would have permitted them to clarify the position with Lady Brittan, for which the (Met) apologised in a letter to her solicitors on 6 October 2015," the force added.
Scotland Yard's report said criticism of its handling of previous allegations against well-known figures had dictated its actions in reviewing the case against Lord Brittan, who served in the cabinet under Margaret Thatcher.
An appeal was sent to the Crown Prosecution Service (CPS), delaying a result in the investigation, despite the Met's conclusion there "was not a strong case against Lord Brittan" and the CPS ruling that the initial police file "lacked sufficient evidence to charge a suspect".
The appeal was lodged in November 2014 but not followed up formally in writing until two days after Lord Brittan's death in January this year.
"Lord Brittan could not therefore, at that point, have been informed that no action was to be taken in respect of this allegation," the Met said.
The report also accepted it was via the media that it became first aware that Tom Watson had written to the Director of Public Prosecutions (DPP) regarding the allegations - 16 days before the investigation's commander received a copy of the letter from the CPS.
The force confirmed commissioner Sir Bernard Hogan-Howe has asked a separate force to "review this investigation to ensure it was thorough, properly conducted and to identify good practice".