Deputy Commissioner Nick Kaldas – feted locally and internationally – will have the full extent of historic corruption allegations against him laid bare at a public inquiry.

Detailing the potentially explosive and damaging claims will be his fellow deputy, Catherine Burn – the officer who led an internal affairs probe which placed Kaldas under covert surveillance more than a decade ago.

For all involved – and the NSW government – the stakes could not be higher.

The professional futures of Kaldas, Burn and even perhaps the retiring police commissioner Andrew Scipione hang in the balance.

The outcomes of this inquiry and of a parallel, behind-closed-doors investigation by NSW Ombudsman Bruce Barbour, are likely to determine whether Kaldas, Burn – or as seems increasingly likely, neither – is appointed to the top job of commissioner.

Scipione, commissioner since 2007, is facing serious questions about his handling of the scandal, which involves the potentially illegal or improper bugging of more than 100 police and a journalist.

Meanwhile, the judgment of the NSW Police Minister, Stuart Ayres, and Premier Mike Baird is being drawn into question as they refuse to respond to sensational evidence emerging from the inquiry's first four hearing days.

The internecine politics of the NSW Police have arguably not been so publicly on display since the landmark 1995 Royal Commission into corruption in the force.

This time, however, it is senior cop against senior cop. The immediate risk of reputational damage is apparent: how can the police force possibly function adequately when three of its most senior officers are at each others' throats?

But it is the immediate aftermath that also has many worried. If the scandal claims the careers of Kaldas and Burn, the NSW Police Service will have lost two of its most experienced and, to date, respected operators.

The professional rivalry between Kaldas and Burn has been apparent for some time.

When Peter Ryan stood down as NSW police commissioner in 2002, his deputy Ken Moroney was seen as the obvious choice as his successor. When Moroney retired in 2007, Scipione was clearly the prime candidate, with many of his potential rivals falling by the wayside.

But as Scipione prepares to stand down, which he has indicated will most likely occur this year, the matter of his successor has not been as clear cut.

It is understood that the state government has favoured Mr Kaldas. A popular figure-head among the troops, he is also a decorated detective and hostage negotiator as well as having spent a year leading the United Nations investigation into the assassination of Lebanese president Rafic Hariri.

He was appointed deputy commissioner in 2007, along with the since-retired Dave Owens.

But almost since her promotion to deputy commissioner in 2010, there has been a suggestion that Scipione has favoured Burn and sees her as his obvious successor.

A former local area commander at Burwood and Redfern, who has also spent time in charge of the internal affairs branch, she would also become the first female police commissioner in NSW history.

Scipione was only too aware of this perceived favouritism towards Burn ahead of Kaldas when he gave evidence at the upper house inquiry this week. "To suggest I had favoured one over the other is simply not true," he told the hearing.

Scipione also admitted publicly for the first time what has long been known – that there is clear tension and conflict between Kaldas and Burn.

That tension has been simmering since well before they were rivals for the top job.

The conflict dates back to an allegedly covert investigation into allegedly corrupt police, code named Mascot, run by internal affairs and the NSW Crime Commission between 1999 and 2001.

Burn was a team leader in the Mascot investigation. Mr Kaldas was one of the targets.

Central to the investigation was a serving NSW police officer, code named M5, who wore a wire to bug his colleagues.

Some listening device warrants obtained by internal affairs and the commission contained more than 100 names, mainly of former and serving police.

Among those names was Mr Kaldas – who appeared on some 80 warrants.

But in many cases the affidavits presented to Supreme Court judges contained no information whatsoever that would justify the bugging.

Many police targeted by the investigation believe numerous criminal offences have been committed by internal affairs and crime commission officers attached to Mascot.

Kaldas, who has said he and his family were subjected to two years of intensive surveillance by Mascot with no accusation made against him, has labelled its work "at best improper and probably illegal".

Adding to the tension is that Scipione was commander of internal affairs from early 2001 and for a short period of time had oversight of Mascot.

A scandal blossomed soon after. Complaints about Mascot were investigated by an internal taskforce launched in 2003, Strikeforce Emblems. But its efforts were stymied by a refusal by the crime commission to release key documents, such as affidavits, citing secrecy provisions.

The Emblems report was never publicly released. But in 2012 Fairfax Media began publishing extensive details, prompting pressure on the government and the police executive for answers.

Shortly afterwards then NSW Premier Barry O'Farrell introduced legislation to parliament granting the Ombudsman special powers that overrode secrecy laws, to investigate.

But mid-last year complaints began emanating from those who were being interviewed by Barbour, claiming he was focusing on finding the source of the leaked documents at the expense of the broader inquiry.

The complaints led to the current parliamentary inquiry – largely due to the agitating of Kaldas, who approached inquiry chair Robert Borsak to seek his assistance.

So what is Kaldas playing at? From any perspective, it's a highly risky move to invite a rival to air corruption allegations against him in the full glare of a high profile public inquiry.

Some speculate it may speak to how desperate Kaldas is for a chance to drive a stake through the heart of the allegations that have stalked him for so long.

Others suggest Kaldas is using the inquiry to publicly clear his name to keep him in contention for the commissioner's job.

What exactly is about to be aired in public is unclear, but the hearings to date have offered some indication of the type of allegations likely to be laid on the table on Tuesday.

In his first round of evidence, Kaldas outlined two allegations he understood to have been made against him, each dating back about 25 years, to when he was a junior officer.

Details are vague, but one related to the arrest of a person later convicted of armed robbery. The other also involved an armed robbery and "an allegation that somebody had stolen money at a search warrant".

This week, we got some more detail when the former director of the NSW Crime Commission, John Giorgiutti, gave evidence.

Giorgiutti – who had in 2012 reviewed a file of allegations against Kaldas compiled by the Mascot team to justify its bugging of him – recounted how Kaldas was accused of "loading up" a suspect with a gun at a cemetery.

However, Giorgiutti said he was sceptical of the claim as the suspect was not at the cemetery when the incident was supposed to have happened. He said the allegation was "disposed of" in related court proceedings.

That might have been the extent of it, but for a period of questioning during Burn's evidence on the inquiry's second day.

Burn was asked to justify declaring in a briefing to her then commander that Kaldas was "suspected to have been involved in or have knowledge of corrupt or criminal conduct by police".

She responded that she had "reasonable suspicion" and "I do have reasonable belief" but wasn't sure she should be outlining the basis for those in public and offered to give evidence to the committee in private.

It was this that provoked Kaldas' lawyer, Robert Ishak, to ask the inquiry to recall Burn so she could be "compelled to identify her allegations, with precision and in an open forum, so as to allow Deputy Commissioner Kaldas to respond".

As for Burn, the inquiry heard evidence she was one of two police who interviewed M5 and specifically asked him about Kaldas. They did not raise the name of any other officer with their informant. She will almost certainly be asked to explain this on Tuesday.

She has denied being part of a vendetta against Kaldas or ordering false affidavits to be sworn.

The government says its opposition to the parliamentary inquiry is due to Barbour's assertion that the public hearings could derail his own investigation, due for completion in June.

But inquiry deputy chair David Shoebridge believes more can be done.

"The government should be telling the public what steps they are going to take to resolve the unacceptable dysfunction at the top of the police force," he says.

Baird, though, is refusing to act on the strength of what has emerged so far. He has continued to back Scipione even after criticism that the commissioner failed to take any steps to resolve the matter for five years on his watch.

"I need to see all of the facts before we take any action," Baird said.

That means the government is determined to wait for Barbour's report before taking steps.

The question now is whether Tuesday's showdown will do anything to change that.