The doomed 16-month investigation, sparked by false accounts given by fantasist Carl Beech, saw raids on the homes of former home secretary Lord Brittan, as well as D-Day veteran Lord Bramall and ex-Tory MP Harvey Proctor
Operation Midland ended in 2016 without a single arrest, after Beech made a series of lurid claims, all later proved to be untrue, including three murders.
Lady Brittan told the Home Affairs Select Committee on Wednesday: “I perfectly accept that the (Met Police) Commissioner came and offered me a very fulsome apology.
“But in the end there are issues at the back of all of this as far as the moral compass of the police is concerned which I think have not been addressed.”
She added: “I just feel that all these years on, and particularly for the family of Lord Bramall, because after all he has died, there hasn’t been much justice.”
The Metropolitan Police was heavily criticised for having believed Beech too readily despite inconsistencies in his evidence including naming witnesses that did not exist.
Lady Brittan told the committee: “I find it quite extraordinary when you look at the unfolding of the events, in a funny way that anybody could have believed any of it at the very beginning.
“If you look at those who were accused, the fact that they were busy people at the top of their tree, and yet they were accused of finding time to have two hours off every afternoon doing what they shouldn’t be doing.
“I come to the view that none of the things that should have been done in order to try and test the evidence the other way were done.”
One of the most serious accusations levelled at investigators was that they allegedly misled a district judge when applying for search warrants.
An independent review into the case by former High Court judge Sir Richard Henriques claimed that the judge had been knowingly misled.
Despite this, police watchdog the Independent Office for Police Conduct (IOPC) cleared the five officers involved in the application of any wrongdoing.
Lady Brittan, who was a magistrate for 26 years, told the committee that the warrants had been used as “a fishing expedition”.
She said: “Of all the things that went horribly wrong in that particular inquiry was the application for search warrants.
“In my view at the time, because I’ve signed search warrants in the past, it was a fishing expedition, and that’s really not what you’re allowed to do with search warrants.”
The 80-year-old, whose homes were searched six weeks after her husband died, added: “It is the greatest invasion of your privacy and in fact in the end it is a trespass on your property. This makes search warrants such an important part of the legal process.
“In this case I just didn’t feel that particular aspect and the terrible consequences of what a search does to the people concerned, and indeed to the subsequent press coverage, that wasn’t taken into account at all.”
Lord Brittan was investigated under Operation Midland as well as a second allegation, Operation Vincente, that he had raped a 19-year-old woman in 1967.
Lady Brittan was later told that there would have been no case to answer for her late husband under either investigation.
She said that the police complaints process was “unbelievably opaque”, and that the IOPC lacked teeth.
She said: “It discourages people to make complaints if the system is so opaque that you really don’t know what you’re going to get out of it and what you’re going to put yourself through.”
Lady Brittan added: “It really has to be able to say we have teeth which we can use, because if you don’t have teeth what is to stop the organisation which you’re regulating just going on as it has gone on because nobody really will ever hold it to account.”
In a written statement published on the committee’s website, Lady Brittan said the police watchdog’s report on Operation Midland “lacked rigour and could fairly be described as a whitewash”.
She said the document “demonstrated that the IOPC has inexperienced investigating officers who are not familiar with the criminal law or the requirements of the Police and Criminal Evidence code of practice on search warrants, and lack the necessary investigative skills”.
The statement also described how she felt “tricked and harassed” after comments she made to watchdog investigators who visited her home were construed as complaints.