Accused in the Australian Parliament of covering up sexual assault, Adelaide's vicar-general, Monsignor David Cappo, quit as head of the Mental Health Commission Thursday.

In a statement, Cappo declared that his remaining in a government post be a distraction amidst the allegations unleashed by Independent Senator Nick Xenophon that he ignored complaints of sexual abuse endured by John Hepworth as a seminarian in the 1960s.

According to Xenophon, Hepworth was abused by two students and a priest over 12 years while studying and training as a Catholic priest. He was eventually ordained but later converted to the Anglican faith in the 1970s.

In a report by the Agence France-Presse, Xenophon accused Cappo of sitting on the 'rape charges' that Hepworth had allegedly lodged to his office in 2007, prompting the senator to question the Catholic official's qualification as a mental health chief.

Cappo denied any wrongdoing in on the matter, which is now the subject of an archdiocesan inquiry.

"This matter has the potential to distract from the important work of the newly formed Mental Health Commission. I cannot allow that to occur," Cappo sads.

The cleric will also leave his other position as deputy chief of the government's social inclusion policy panel.

His resignation though does imply any admission of culpability, Cappo stressed as he emphatically rejected "any suggestion that I or the church handled the complaint by John Hepworth with anything other than proper and due diligence."

On Tuesday, Xenophon tagged Monsignor Ian Dempsey, who now serves as a parish priest in South Australia, as one of the perpetrators of the sexual assault some four decades ago, with two others now deceased.

Dempsey, however, described Xenophon's claims as unfounded. He said they were based on Hepworth's sketchy accounts of events that may have transpired some 45 years ago.