Brighton-based Sussex Police officer Tony Lumb was arrested on suspicion of misconduct in public office in March 2017 and was suspended from the force.
The police watchdog investigated, found evidence to suggest a criminal offence may have been committed and referred the case to the Crown Prosecution Service (CPS).
The former elected member of the local Police Federation inspector's branch board was questioned over allegations he had improper sexual relations with women in the course of his duties. He was released on bail after being interviewed under caution.
In October, after nearly a year of discussions, the CPS said there was insufficient evidence to justify a prosecution and decided to take no further action.
One of the complainants, Nicola Brookes, branded the decision ‘shocking’ and called for it to be reviewed.
But this week the CPS confirmed it would not proceed with the case after considering the evidence for a second time under the Victims' Right to Review scheme.
In a letter explaining the decision, the CPS said it took ‘careful and fully independent consideration of all the available evidence’.
In the letter, seen by the Press Association, specialist prosecutor Fiona Morrison said: ‘Having considered all the available evidence, I have concluded that there is insufficient evidence for there to be a realistic prospect of conviction of Inspector A for the offence of Misconduct in Public Office.
‘I realise that you are likely to be very disappointed with the decision I have reached but I am grateful that you felt able to raise your concerns about this case with the CPS.
‘It is through such direct contact that we are able to ensure that prosecutors are making the right decisions and that we identify all opportunities for improving our service to the public.’
On hearing the news Ms Brookes said she felt there had been a ‘massive injustice’, and that she was considering a civil case against the authorities.
The 52-year-old, who lives in Brighton and has Crohn's disease, reiterated previous criticism that the entire process, including the review, had been fraught with delays and said she feared for the safety of other potential victims who report allegations of crime to police.
The Independent Office for Police Conduct (IOPC) also found Lumb - who previously denied the allegations - had a case to answer for gross misconduct.
He is now set to face force misconduct proceedings.
An IOPC spokesman said: ‘The independent investigation into allegations a Sussex Police inspector engaged in improper relationships with women in the course of his duties concluded in October 2017.
‘A file of evidence in relation to the actions of the officer was then referred to the Crown Prosecution Service.
‘We are aware of the CPS decision to take no further action in this case.
‘At the conclusion of our investigation we shared our findings with Sussex Police who agreed that the officer has a case to answer for gross misconduct. It will now be for Sussex Police to schedule a hearing to take place.’
Abuse campaigner Ms Brookes won a landmark High Court case in 2012 which forced Facebook to reveal the identifies of trolls who vilified her when she posted a comment supporting former X Factor contestant Frankie Cocozza.
In August last year, she saw internet troll Nicky Wright - who stalked her online, unleashing a torrent of abuse on a daily basis for more than a year - jailed but he was released early.