The police investigation into alleged sex abuse by Lord Brittan was "fully justified" - though the case was unlikely to result in a criminal conviction - a review has concluded.
Lord Brittan died a year ago still under suspicion of being part of a VIP paedophile gang.
A lack of primary evidence in the case meant he was cleared by the Met of rape, though he died from cancer aged 75 without being notified of the decision. The way the Metropolitan Police handled the investigation has resulted in criticism for its commissioner Sir Bernard Hogan-Howe.
A review by Dorset Police has since vindicated the decision to investigate a rape claim by a student against Lord Brittan, dating back to 1967, but said any court case would likely result in an acquittal rather than a conviction.
The review said: "An investigation into allegations made by the complainant was necessary, proportionate and fully justified despite the significant passage of time."
It said the police log "was not a comprehensive document and omitted key elements of decision making" and lacked essential detail.
It also found a "poor standard" of obtaining evidence to be used in the case, and said the senior investigating officer made errors and was "inexperienced in rape investigation".
But the review also broadly supported the investigation.
It said: "Skilful investigators pursued appropriate lines of inquiry from the complainant's account and obtained credible evidence.
"At the conclusion of these lines of inquiry, any reasonable investigator could properly conclude that the allegations made by the complainant were far from fanciful and continued to be proportionate and justified."
It described the complainant, a 19-year-old woman, as a "competent witness" who displayed "no malice" in her motivation. She had "little to gain from making a false allegation", the review added.
There was "some ambiguity surrounding the issue of consent" to have sex, which would prove difficult before a properly directed jury.
The review added: "Proving that consent was not given or could have reasonably been implied would be the first difficult step and proving that LB (Lord Brittan) understood this to be the case would have proved more difficult still.
"When all these factors are taken into account, the reviewer concludes that following a thorough investigation with no useful lines of inquiry left unexplored, the case is more likely to lead to acquittal than conviction."
It said the investigation was conducted "with integrity, proportionality and objectivity ... in good faith, against a credible account provided by a compelling witness".