The high-ranking officer expressed concern regarding the direction the Ombudsman’s inquiry, known as Operation Prospect, had taken and the lack of welfare available to those called to appear before it.

The NSW Police Association has raised similar concerns, urging the Ombudsman, Bruce Barbour, to publicly confirm witnesses ‘‘in a heightened state of stress and anxiety after being involved in an investigation that has been ongoing for 16 years’’, would get access to appropriate medical treatment.

There is now a NSW upper house inquiry into Operation Prospect and the Ombudsman’s handling of it.

The officer, who spoke to the Mercury on condition of anonymity, said faith in Operation Prospect had been lost and its eventual findings compromised.

Prospect is investigating the 1999-2001 bugging operation code-named Mascot targeting allegedly corrupt police, which has already been the subject of previous failed inquiries.

‘‘I’m worried about [some] of our blokes who are almost suicidal from what this has done to them,’’ the officer said.

Mr Barbour said in a written submission to the upper house inquiry  there were ‘‘at least eight witnesses who advised Operation Prospect that they suffer from a mental health condition in some cases related to  Mascot’’.

A further four witnesses provided medical reports indicating they were too unwell to give evidence.

Two of those were excused, one was excused mid-hearing ‘‘when it became evident he was experiencing difficulties’’ and the other was excused from further attendance on the basis of a medical certificate issued after his first evidence.

The senior officer told the Mercury the negative impact of the drawn-out proceedings on officers was real.

‘‘One bloke had to be carried out, he effectively couldn’t finish his evidence.

‘‘He was perfectly normal before this, he is a retired distinguished cop who was dragged down there repeatedly and is still continuing to be dragged down there and he’s got nothing to do with anything.’’

Mr Barbour has the power to override secrecy laws to investigate allegations of misconduct by police,  the NSW Crime Commission and the Police Integrity Commission relating to investigations between 1998 and 2004.

But people being interviewed by Mr Barbour fear Operation Prospect has become a quest to shut down and identify whistleblowers who are alleged to have leaked confidential information.

‘‘He’s got secrecy provisions harsher than any other body, he can’t be sued, even after he retires,’’ the senior officer said.

‘‘He has no inspector looking over his shoulder, unlike the PIC [Police Integrity Commission] and ICAC, he can bypass the right to silence whenever he wants to.

‘‘But probably the biggest dilemma at the moment for all of us is that he has responsibility in the state of NSW for protecting whistleblowers.

‘‘You cannot be on the one hand investigating corruption and wrongdoing, systemic corruption, and at the same time persecute those who brought it out into the open. You surely can’t do both.’’

Mr Barbour has rejected as ‘‘false’’ and ‘‘baseless’’ claims his inquiry is targeting whistleblowers, declaring it a ‘‘rigorous’’ and impartial search for the truth.

On Tuesday the inquiry will hear from two NSW Police deputy commissioners at the centre of the drama, as they go head to head over 15-year-old allegations.

Catherine Burn has been recalled before the inquiry and will be examined regarding the ‘‘suspicions’’ she had that led to the investigation of her colleague Nick Kaldas.