Barnaby Joyce is still under investigation over parliamentary expenses claims, despite quitting as deputy prime minister.
But the ex-Nationals leader is no longer facing a formal review of whether he broke the ministerial code of conduct.
Prime Minister Malcolm Turnbull asked top bureaucrat Martin Parkinson on February 21 to investigate whether Mr Joyce breached the code, before the Nationals leader resigned from the role on February 23.
Mr Joyce faced 16 days of allegations about his behaviour and use of parliamentary expenses after his affair with now-pregnant former staffer Vikki Campion was revealed.
"There were constant claims that the member for New England had been in breach of the statement of ministerial standards but no particulars were being given," Mr Turnbull told parliament on Monday.
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The prime minister told Mr Joyce about the review on Wednesday, but Dr Parkinson wrote to him on Monday to say there was little to be gained considering Mr Joyce went to the back bench on Friday.
"I note, however, that the audit into the use of travel and travel-related expenses by Mr Joyce and Ms Campion by the Independent Parliamentary Expenses Authority is ongoing," Dr Parkinson said in his letter.
Mr Joyce cited allegations of sexual harassment - which he denies - as the final straw that led him to resign.
Catherine Marriott, a former West Australian Rural Woman of the Year, accused Mr Joyce of sexual harassment, but says she never intended for the allegations to go public.
Nationals federal president Larry Anthony confirmed he asked for her complaint against Mr Joyce be made in writing, but he insists he did not leak it.
"The confidentially that we were imposed on, by her solicitor and mine, we have kept," Mr Anthony told Sky News on Monday.
He said three high-ranking Western Australian Nationals told him about the allegation on February 19.
"I said to them, well if this is a substantial complaint then it needs to be put in writing," he said.
"It wasn't as if this was a secret. It was well known by the WA National Party."
Victorian Nationals MP Andrew Broad on Sunday night suggested the Liberal Party leaked the details of Ms Marriott, but he would not name names.
Cabinet minister Mathias Cormann, who was acting prime minister last week, said he was not aware how the allegations became public and didn't believe any Liberals were aware of the specifics.
Ms Marriott broke her silence on Saturday and said she never intended the explosive allegations to go public.
She had asked the party to undertake a formal and confidential investigation to ensure there was accountability.
Mr Joyce called the allegations "spurious and defamatory" when he resigned on Friday, and called for them to be referred to police.
