New Zealand’s government will take the unprecedented move of appointing an inspector general of police after a damning report found “significant failings” in the way senior police officers handled serious sexual complaints against a former high-ranking officer.

The Independent Police Conduct Authority (IPCA) released a 135-page report on Tuesday detailing allegations made against the former deputy police commissioner Jevon McSkimming and the police’s response to them.

In a separate matter, McSkimming last week pleaded guilty to possessing child sexual exploitation and bestiality material.

Tuesday’s IPCA report said that rather than investigating allegations made against McSkimming, the police used accusatory emails sent by the complainant, known as Ms Z, to charge her with sending harmful digital communications.

The report found there were “significant failings” in the police response to the complaints, which were characterised by inaction and “an unquestioning acceptance of Mr McSkimming’s narrative of events”. It recommended a revamp of police policies, more robust processes around alleged police misconduct and enhanced oversight.

“It’s atrocious on every level,” Mark Mitchell, the police minister, told broadcaster RNZ on Wednesday.

Mitchell said the report highlighted “significant flaws” in the decision making, judgment and actions of police, including former leaders.

“Their actions have raised serious concerns about integrity and culture within the then executive,” he said.

Mitchell said the appointment of an inspector general would help ensure police followed proper procedure and restore public confidence in the police.

The allegations arose from a sexual relationship that began in 2016 between McSkimming, who was then 40, and Ms Z, an unsworn police staffer who was then 21, the report said.

After the relationship ended in 2018, McSkimming informed senior police staff of their affair and told his supervisor Ms Z was threatening and blackmailing him.

From 2018, Ms Z allegedly sent hundreds of emails to McSkimming and other police staff, made various posts to social media and lodged complaints with the police hotline, detailing allegations against McSkimming, including of sexual interaction without consent and threats to use intimate video recordings, the report noted.

In January 2024, Ms Z’s emails were used to charge her with harmful digital communication towards McSkimming. The charges were later withdrawn.

Police decided to investigate Ms Z’s allegations a month after charging her, but the IPCA found the investigation process sat “in stark contrast” to the police’s usual practice, and the future of McSkimming’s career was prioritised.

The report found Andrew Coster, the commissioner at the time, “attempted to influence the nature and extent of the investigation” and, during the deputy commissioner appointment process, failed to disclose to the Public Service Commission his knowledge of McSkimming’s relationship.

The Guardian contacted McSkimming’s lawyer for comment. Coster declined to comment.

The current police commissioner, Richard Chambers, described the actions and attitudes laid out in the report as “inexcusable” and apologised to Ms Z, who he said was ignored and badly let down.

“The ambitions of a senior police officer were put above the interests of a vulnerable woman.”