The head of the journalists’ union has said he doesn’t believe The Australian reporter Cameron Stewart breached any ethical undertakings to his source during the Victorian Office of Police Integrity investigation into the scoop on the Operation Neath anti-terrorism raids.

This follows OPI lawyers asserting during the so-called Ozleaks case that the key piece of evidence to be used to prosecute Stewart’s alleged source was a record of interview with Stewart in which evidence had been given voluntarily — meaning it was able to be used in court.

Chris Warren’s opinion on Stewart’s ethical conduct was first made public in this piece in Monday’s Australian — but given that other aspects of this article were, to my certain knowledge, inaccurate, I wanted to check that Warren had been accurately quoted. He has been hard to contact, but yesterday I was able to talk to him and gain some more details.

Warren told me Stewart had approached him in the wake of the OPI assertions. Stewart’s briefing of Warren was constrained by the legal limitations he was under, which restrain individuals from disclosing what occurs during OPI investigations.

But, Warren said, as a result of the briefing “I don’t believe that [Stewart] at any stage breached his undertaking to maintain the confidentiality of the source”.

So was the OPI lying or incorrect? Or was there some other factor in play?

Warren would speak only generally. Emphasising that he was not necessarily commenting on the Stewart case, but only on “pure theory”, he said sometimes a source might give information “off the record” but later agree to release the journalist from their obligations to maintain the confidence.

“It is also generally accepted that the obligation ends if the source dies, for example,” Warren said.

Meanwhile, I understand prosecuting authorities have now been briefed by the OPI, and charges against the alleged source — a Victorian police officer — are imminent. I also understand that only a small part of Stewart’s information is alleged to have come from this source, with the rest being provided by the Australian Federal Police after Stewart approached them with what he knew.

The charges relate to Stewart’s scoop of August last year, in which he broke news of an anti-terrorism operation on the very day that raids were conducted and arrests made. Later that day Victorian Police Commissioner Simon Overland slammed the paper and by implication the AFP, saying the publication had put the operation and officers’ lives at risk.

These events, and the investigation in to the leak, were the genesis of the media war between The Australian on the one side and the OPI and Overland on the other that we have seen unfold over recent weeks.

The circumstances of Stewart’s briefings from the AFP are presently being investigated by the Australian Commission for Law Enforcement and Integrity. As I have written previously, the identity of the officer alleged to be Stewart’s source is an open secret in Melbourne journalistic and police circles. He had been quoted in a previous article by Stewart. I understand that an email trail will also be part of the evidence in the case.

Stewart did not respond to a message I sent him yesterday, but he has previously declined to comment for legal reasons.