An Australian lawmaker has threatened to name and shame a Catholic priest accused of violently raping an Anglican archbishop in attacks that allegedly started about 50 years ago.

Independent senator Nick Xenophon said the Church must stand down the priest or he would name him in parliament in connection with the alleged sexual abuse of Archbishop John Hepworth.

Hepworth, who was trained and ordained as a Catholic but shifted to the Anglican church in the 1970s, claims he was violently raped and sexually abused over 12 years from age 15 by two priests and a seminary student.

Two of the men are now dead but the third runs a parish in South Australia state, where Xenophon said he was being protected and allowed to practise despite Hepworth's allegations, which he first raised with the Church in 2007.

Xenophon told parliament there were "parents sending their children to church unaware that their priest... has been named as an abuser" and threatened to out the accused man if Adelaide's Catholic diocese did not stand him down.

Lawyers for the diocese countered with a strongly-worded letter urging him to desist from his threat while defending their decision not to suspend the priest as consistent with both religious and procedural law.

"You may be aware that the allegations made by Archbishop Hepworth relate to a period dating back almost 50 years," the lawyers said.

"The priest concerned has categorically denied the allegations and, objectively speaking, it is not irrelevant that he has been a priest of good standing in the archdiocese for almost 50 years."

Xenophon vowed to press ahead and identify the man Tuesday evening, saying the Church had left him with "no choice".

"My next move is to discuss this matter in the Senate tonight," he told reporters.

"If this priest is named tonight in the Senate, the Catholic Church in South Australia will only have itself to blame."

Xenophon earlier warned that the case had grave implications for the besieged Labor government, which appointed top South Australian Catholic official Monsignor David Cappo as chief of its new Mental Health Commission.

"Monsignor Cappo, for reasons not fully explained, has failed to act in a timely and decisive manner on this important issue," he said on Monday, adding the matter had been given a "seemingly low priority" by the Church.

"I question whether it is appropriate for a senior religious figure like David Cappo, who has responded this way to allegations of serious sexual and psychological abuse, to be given the role of chairman of the federal government's mental health taskforce," he said.

Hepworth, head of a breakaway Anglican group seeking reconciliation with the Vatican, said he was "saddened" by the "very crude way" the issue was now playing out, describing it as "megaphone diplomacy".

He raised the matter in public for the first time after decades of silence with a media interview on Saturday.

The interview followed an apology and offer of Aus $75,000 compensation from the Archdiocese of Melbourne in relation to the two men he accused of abuse who are now dead.

Hepworth, 67, has not sought to bring criminal charges over the case.

Sign up to our free newsletters

Get the best updates straight to your inbox:
Please select at least one mailing list.

You can unsubscribe at any time by clicking the link in the footer of our emails. We use Mailchimp as our marketing platform. By subscribing, you acknowledge that your information will be transferred to Mailchimp for processing.