Days after Ms Higgins publicly revealed her allegation she had been raped in the office of Minister Linda Reynolds by a fellow former staffer in 2019, Channel Ten journalist Peter van Onselen said on the ABC that members of the Prime Minister's media team had been briefing journalists against her partner, David Sharaz.

Scott Morrison referred the allegation to his chief of staff, John Kunkel, who made his findings in a letter to Mr Morrison dated Tuesday, May 25 and tabled in the House of Representatives.

"On the first-hand evidence before me, however, and bearing in mind the seriousness of the allegation that you have asked me to investigate, I do not make a finding that negative briefing against Mr Sharaz of the sort alleged has taken place," Dr Kunkel wrote.

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"In the context of my inquiry, such a finding would be based upon hearsay (in some instances, second- or third-hand).

"The evidence before me falls well short of the standards that would be needed to arrive at such a finding in conformity with due process."

However Dr Kunkel did not find Ms Higgins or others were not being truthful about the allegation.

"In arriving at that conclusion, I stress I do not deny that the beliefs of Ms Higgins are sincerely held. Plainly, they are. My conclusion, based upon the evidence presented to me, should in no way be taken as a reflection on the honesty and sincerity of Ms Higgins."

That the allegations were made at all was a concern, Dr Kunkel said.

"While I am not in a position to make a finding that the alleged activity took place, the fact that those allegations have been made serves as an important reminder of the need for your staff to hold themselves to the highest standards."

In the process of writing the report, Dr Kunkel said he had been contacted by a member of the press gallery after the Prime Minister gave an interview on the ABC's AM program on March 25, as well as a letter from Ms Higgins, that said she had been made aware by "numerous" journalists that members of the Prime Minister's media team were backgrounding against her partner, painting him as a "disgruntled" former public servant.

Dr Kunkel said he interviewed members of the Prime Minister's media team, and said "all senior members of the media team rejected the allegation of backgrounding with the purpose of undermining the reputation of Mr Sharaz".

He also interviewed members of the press gallery, some of whom referred to "corridor conversations" about the allegation by Ms Higgins, and while three journalists said they had been told of the backgrounding, none had been briefed themselves.

The individual who contacted Dr Kunkel on March 25 then decided to take no further part in the process.

Earlier, Labor had named members of the Prime Minister's staff during a feisty Senate estimates hearing.

Labor's Katy Gallagher had said one journalist who came forward and forced the hand of the Prime Minister to launch the investigation had since withdrawn their evidence.

She questioned why Dr Kunkel would ask the victim of an alleged rape at Parliament House in March 2019 to now demonstrate that the backgrounding occurred.

"This looks like an attempt to push back on Ms Higgins very strongly and it seems extremely unfair to me," Senator Gallagher said.

- With AAP

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