The deputy Nationals leader resigned on Sunday, after Mr Gaetjens found Senator McKenzie had breached ministerial standards by failing to recuse herself when awarding grants to gun clubs she had a connection to.

However Mr Gaetjens absolved Senator McKenzie of the most serious allegation - that she used the $100 million Community Sport Infrastructure Grant program to funnel money to seats the Coalition wanted to win at the 2019 election.

This stands in stark contrast with the findings of the Australian National Audit Office, which uncovered a "distribution bias" in the way the senator and her office doled out money.

The results were convenient for the Prime Minister's office, which had been facing its own barrage of questions over its alleged involvement in the grants program.

There was also a cloud over Mr Gaetjens himself, given he worked as Mr Morrison's chief of staff from October 2015 to June 2018.

But a spokesperson from the Department of the Prime Minister and Cabinet rejected any allegations of impropriety.

"Mr Gaetjens is a long-standing public servant who has served, and continues to serve, the government of the day impartially and professionally," the spokesperson said.

"Like many senior public servants, his career has included periods working for ministers.

"His past employment, as chief of staff to Mr Morrison when he was Treasurer, is well known, and does not constitute a conflict of interest in the context of providing the Prime Minister with advice in relation to the application of the Statement of Ministerial Standards."

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Mr Gaetjens is not the only departmental secretary to have done a tour of duty as a political staffer.

Former Department of the Prime Minister and Cabinet boss Martin Parkinson worked as an adviser in the Keating government.

Recently ousted Agriculture boss Daryl Quinlivan and Communications secretary Mike Mrdak also worked as government staffers in the Keating government.

Both Attorney General's department head Chris Moraitis and Home Affairs secretary Mike Pezzullo worked for former Labor foreign minister Gareth Evans.

And Department of Foreign Affairs and Trade secretary Frances Adamson worked for Labor foreign affairs and defence minister Stephen Smith.

Meanwhile the government is still refusing to release Mr Gaetjens report, citing cabinet confidentiality.

Martin Parkinson's advice on Christopher Pyne and Julie Bishop's post-ministerial jobs was tabled in the parliament.

However it is understood that only advice for former members - not current - can be released.

Advice on ministerial standards has been sought seven times since 2013, excluding the McKenzie case.

When the advice related to a sitting member - namely Jamie Briggs, Stuart Robert, Sussan Ley and Barnaby Joyce - the advice was not made public.

However when the advice was about post-ministerial employment - specifically Andrew Robb, Bruce Billson as well as Mr Pyne and Ms Bishop - it was tabled in parliament.