A canon law specialist says Catholic bishops in Australia are still obliged to not report child sexual abuse to authorities in jurisdictions without mandatory reporting laws.

A confidential instruction from the pope in 1922 directed bishops to treat canonical crimes such as "obscene acts with animals", "solicitation of sex during confession", and "gravely sinful offences perpetrated against children" with the utmost secrecy.

"And that secrecy has been confirmed, continued by every pope since, including the current one, Pope Francis," said Kieran Tapsell, an expert witness on a 2017 royal commission panel on canon law.

When bishops from across the country meet in Melbourne this week, they are expected to decide how to respond to the Royal Commission into Institutional Responses to Child Sex Abuse recommendations.

The Catholic Church has already made its stance clear on some of the royal commission's more contentious recommendations — such as the strengthening of state mandatory reporting laws to include information revealed in the confessional, which it opposes.

But it has not yet revealed its stance on recommendations aimed specifically at its own operations as a religious institution, including a 20th century element of canon law now known as the "pontifical secret".

"Because of all of this concentration on confession, people don't realise there is still a requirement in canon law to cover up child sexual abuse, within the church," Mr Tapsell said.

"It's still there in black and white. Pope Francis has been asked to change it and he's refused."

Kieran Tapsell (far right) in the Springwood seminary in New South Wales in 1963. ( Supplied: Kieran Tapsell )

Separation of church and state led to 'defensive' culture

Mr Tapsell is a retired civil lawyer who spent six years training to enter the priesthood in the 1960s.

He said he started researching canon law when one of his seminary professors got caught up in a child abuse scandal in New South Wales.

Mr Tapsell said the 1922 directive, known as Crimen sollicitationis, or the crime of solicitation, had been reinstated in various incarnations during the 20th century as part of a permanent reversal in attitude from the church that, centuries prior, had willingly handed over sexual predators to civil authorities.

"If you go back to St Basil of Caesarea, his rule for the Eastern Church was that a monk who sexually abused boys was to be publicly whipped," he said.

"He was to have his head shaved, spat upon, kept in prison for six months on a diet of bread and water, and never again associate with youths in private conversation or in counselling them.

"Now that sounds very modern, but we're talking about the 4th century."

Mr Tapsell said as the gap between church and state had widened in the 19th and 20th centuries, the Vatican became defensive.

"You had a change in culture, where the church decided that it had to cover up child sexual abuse, and then it passed a law," he said.

"Now the effect of passing that law is to entrench that culture everywhere, because people are told that's what they have to do."

The Vatican gave a directive in 2010 that "civil law concerning reporting of crimes to the appropriate authorities should always be followed", but not all jurisdictions have those reporting laws. ( Reuters: Stefano Rellandini )

Bishop says law was about confidentiality, not cover up

One of the most catastrophic examples of the Catholic Church's failure to respond to child sexual abuse allegations was in Ballarat, under the 26-year tenure of bishop Ronald Mulkearns.

Former Ballarat Bishop Ronald Mulkearns was not asked whether canon law played into the diocese's "catastrophic" handling of child abuse, when he appeared at the royal commission via videolink in 2016. ( Supplied )

The bishop died in 2016 and was not asked during his brief royal commission appearance two months earlier whether the "culture of secrecy" he presided over had had anything to do with canon law.

But the diocese's current head, bishop Paul Bird, disagrees that the purpose of the law was ever to cover up abuse.

"There are some issues with call for confidentiality, but the question is, those provisions for confidentiality shouldn't work against the care of children," Bishop Bird said.

He supports the royal commission's recommendation that Australian bishops collectively ask Rome to amend the law, "so the pontifical secret does not apply to any aspect of allegations or canonical disciplinary processes relating to child sexual abuse".

"If there's anything in the processes of investigation that should be changed in order to put the focus on caring for children, then that should be done," Bishop Bird said.

Pope refuses to change canon law instruction

The canon law directive to keep allegations involving clerical child abuse confidential became known as the pontifical secret after 1974.

The instruction itself, published in the official acts of the Holy See, was "a legislative document with the force of the law", and remains in place in 2018.

But Catholic priest and professor Ian Waters, who lectures in canon law at the Catholic Theological College in Melbourne, told the ABC there was no compelling evidence to suggest canon law was to blame "for what were terrible human failings".

"In cases of investigating child sexual abuse, pontifical secrecy relates solely to such matters when being investigated in trials conducted in church courts," he said.

"A careful and complete reading of the appropriate canon law — rather than words in isolation — shows there is no prohibition on the reporting of allegations of child sexual abuse to police and other authorities."

But the royal commission's report authors did confirm that when bishops in Ireland and the United States challenged Rome to release them of their obligations to the canon law instruction, their request was flatly refused.

Since 2010, the Vatican has softened the pontifical secret to the extent that bishops have been instructed to follow state or federal reporting laws where they apply.

The royal commission heard the 1974 pontifical secret was "a legislative document with the force of the law", and remains in place in 2018. ( Supplied: Royal Commission )

NSW and Victoria only states to pass 'failure to report' laws

Every state and territory in Australia has now delivered its formal response to the royal commission's recommendations.

The recommendations include measures to extend the list of mandatory reporters to priests, and the introduction of laws that make it a criminal offence for any adult, including religious leaders, to fail to report allegations or knowledge of child abuse to authorities.

So far, only NSW and Victoria have passed laws that create that failure to report offence, although neither law covers information revealed in the confessional — an issue the states have indicated will be worked on at a multi-jurisdictional level.

Federal Attorney General Christian Porter has previously said reporting laws are for the most part a matter for the states, but that laws should operate in favour of protecting children.

Universal reporting laws would override pontifical secret

The commissioners did not make any findings in the final report about "the proper interpretation of canon law in relation to mandatory reporting to civil authorities", but argued that "there should be no provision in canon law that attempts to prevent, hinder or discourage compliance with mandatory reporting laws".

Mr Tapsell said until the states adopted universal reporting laws, there was a risk the pontifical secret would take precedent.

"The pontifical secret would not apply if there was a reporting law which covered every allegation of child sexual abuse within an institution," he said.

The Australian Catholic Bishops Conference said it had started discussions with the Holy See on all the relevant royal commission recommendations, including this aspect of canon law.

Bishop Bird said any changes to canon law would ultimately need to come from the Pope.

"The question then for the Roman authorities is to examine the processes, and see whether anything needs to be changed as far as confidentiality goes," he said.

"As time goes on procedures are changed because people become aware of unintended effects."