The senior detective whose explosive allegations sparked the royal commission into child sex abuse says he has been denied whistleblower status.

Detective Chief Inspector Peter Fox alleged in an interview with Lateline last year that the Catholic Church hierarchy protects paedophile priests, silences investigations and destroys critical evidence to avoid prosecution.

The next week, Prime Minister Julia Gillard announced a wide-ranging royal commission into the institutional responses of organisations to child sex abuse.

With the royal commission to get underway today, Chief Inspector Fox told the ABC's 7.30 program last night that NSW Police have informed him that he will not be considered a whistleblower.

Chief Inspector Fox said that decision leaves him open to litigation.

"It was only this week that I've actually learnt the New South Wales Police Force has decided to decline my provision to classify me as a whistleblower ... [under] public interest immunity," he said.

"They've stated some technical reasons saying that I don't classify as whistleblower and therefore I'm not protected.

"It's a little bit odd. I would have thought it's the very thing this legislation was created for, but that appears to be the stance of the police department at this stage.

"It means that I have probably gone out on much more of a limb in making these comments than I normally would have gone.

"I don't have any legal protection behind the comments I am making and I leave myself open to criticisms and also litigation by other individuals and bodies."

However, a NSW Police spokesman says Chief Inspector Fox is protected under the NSW Public Interest Disclosures Act for some of his statements.

"The officer sought to make several disclosures under the NSW Public Interest Disclosures Act," the spokesman said in a statement after Chief Inspector Fox's interview with 7.30.

"One disclosure was declined because it didn't meet the requirements of the legislation.

"The remaining matters were deemed to be protected disclosures, meaning the officer is afforded protection under the Act.

"In addition, the officer is automatically afforded protection for information disclosures under the NSW Police Act and the force's own internal policies.

"The officer has been informed of these outcomes."

Taking a toll

After first making the allegations on Lateline last year, Chief Inspector Fox said he had been the victim of an internal police smear campaign.

He told 7.30 that coming forward about the allegations has taken a toll on his family.

"It's been quite significant. The impact on my family and myself has been very heavy," he said.

"But we keep coming back to the fact that we at least have a choice in what we are doing.

"A lot of these abuse families haven't had a choice in what has happened to them and they've gone through a lot more hell than what we're going through."

But Chief Inspector Fox says he has "no regrets whatsoever" about his decision to speak out.

"That's something I can say without even pausing to consider the question," he said.

"It was the right decision. Yes, it might have a bit of a cost at the end of the day, but I will never have a regret about the fact that it ended up leading to this royal commission."

'Coming clean'

Preliminary hearings for the royal commission begin today in Melbourne, where the commission's chairman Justice Peter McClellan will provide information on how it will conduct its private and public hearings.

The senior counsel assisting the commission, Gail Furness, will also make an opening statement.

No victims or witnesses will make a statement.

Chief Inspector Fox said the church needs to be "absolutely upfront and honest" when it gets its chance to front the commission.

"There's a lot of public scrutiny and ... a lot of public pressure on the Catholic Church, and that's from Catholics themselves," he said.

"We've seen that the Church is reluctant to cooperate in Ireland and has emptied the pews substantially over there.

"If the Catholic Church in Australia doesn't want to see the same things happening, there's a very strong need for them to show that they are much more willing to, if you like, come clean.

"I think you need to go through that difficult, painful process if you're going to come out the other side and get your house back into order."