Public service commissioner John Lloyd still faces possible investigation over an allegation he breached a code of conduct, it has been revealed.
The acting office holder who received the allegation in January from the Prime Minister's Department, acting Merit Protection Commissioner Mark Davidson, said in a letter on Wednesday he is yet to decide whether to start an inquiry.
His letter to Senate president Scott Ryan and House of Representatives speaker Tony Smith came a day after Mr Lloyd said he was not under investigation. Mr Lloyd had refused to confirm this under repeated questioning by Labor at a Senate estimates hearing on Monday.
Mr Davidson said in the letter, tabled at Senate estimates, he had expected a Merit Protection Commissioner to be appointed in the near future and initially told the person making the allegation it would be referred to the permanent office holder when one was appointed.
"A Merit Protection Commissioner has not been appointed and I have continued to act in the position," he said in the letter.
"In late March 2018 I decided that the allegation needed to be addressed."
Mr Davidson said his substantive role was as an employee in the Australian Public Service Commission.
"In light of any perception of bias arising from my substantive employment in the APSC, in April 2018 I asked a former [agency] secretary to assist me to consider whether the allegation, on its face, warranted the start of an inquiry," he said.
"I have not yet reached a view on whether to start an inquiry. I will advise you if I decide to do so."
A permanent replacement for former Merit Protection Commissioner Annwyn Godwin is yet to assume the role since her term finished in December.
The commissioner, who holds an independent role, conducts inquiries into whether public servants have breached the Australian Public Service code of conduct and shares an office and staff with the APSC.
Department of Prime Minister and Cabinet officials told a Senate estimates hearing on Tuesday its secretary Martin Parkinson referred the allegation to the acting Merit Protection Commissioner a month after receiving it in December.
PM&C; deputy secretary Stephanie Foster would not outline the allegation.
Mr Lloyd has previously denied giving special access and research to the Institute of Public Affairs after Labor last year raised an email he sent to a member of the group with an attachment showing what he described as "generous" provisions in public service enterprise agreements.
When asked at Senate estimates whether he was under investigation on Monday, Mr Lloyd refused to answer and initially said his role required him not to disclose the identity of people subject to an investigation.
He later said he would take on notice the basis on which he could make a public interest immunity claim not to answer questions about an investigation, but did not give a deadline before which he would respond to that question.
In confirming he was not under investigation on Tuesday, Mr Lloyd said he would no longer make a claim to public interest immunity after receiving advice.
Ms Foster told Labor senator Penny Wong at Senate estimates on Tuesday that Mr Davidson was able to conduct an inquiry into alleged breaches of the APS code of conduct by the public service commissioner, and was required to report on its results.
Mr Lloyd is a member of the IPA. Before the Abbott government appointed him APS commissioner in 2014, he was the director of the think tank's work reform and productivity unit.