Mr Turnbull has also confirmed Mr Joyce will act as Prime Minister when he travels to the United States next week, in the face of intense scrutiny of the Deputy Prime Minister's relationship with pregnant former staff Vikki Campion.

Mr Joyce delivered a grovelling apology over the scandal to his Nationals' colleagues in a party room meeting on Monday; while a few colleagues expressed their displeasure with him, the strong view of the majority of his colleagues was that he should remain leader of the party. If, however, allegations about Mr Joyce's use of expenses were to emerge it could spell the end for the member for New England.

Liberals are furious with Mr Joyce's actions, with some telling Fairfax Media they believed he should stand aside for the good of the Coalition.

Federal Labor took the gloves off on Monday and focused its question time attack on Mr Turnbull and Mr Joyce over the affair - particularly the highly paid roles created for Ms Campion in the offices of fellow Nationals MPs Matt Canavan and Damian Drum in the months after the relationship began.

After leaving Mr Joyce's office to work for Senator Canavan in April 2017, Ms Campion temporarily moved back to Mr Joyce's office - soon after Senator Canavan resigned from the ministry in July 2017 because of dual citizenship issues - before moving to Mr Drum's office a few weeks later.

Mr Turnbull said neither he nor his office had discussed Ms Campion's employment by Senator Canavan or Mr Drum with Mr Joyce and that "the Nationals were responsible for decisions relating to staffing ... the PM's Office has an administrative role in informing the Department of Finance of changes".

"The Nationals are provided with a number of personal staff positions as a share of the government's overall staffing pool. The distribution of those staff members between Nationals' offices is a matter for the National Party."

Extraordinarily, the government sought to claim the jobs did not breach the ministerial code of conduct because Ms Campion had not been Mr Joyce's "partner" at the time - even though their relationship had been going on for months and was a key reason she was shifted from the deputy prime minister's office to begin with.

Ms Campion left Mr Joyce's employ in April last year when their affair - which ultimately ended his 24-year marriage - began creating tensions in the office.

The 33-year-old was then given a new well-paid role with Senator Canavan, a close ally and fellow former staffer of Mr Joyce. Reports have suggested the job carried a salary of about $190,000 a year. When Senator Canavan stood aside over dual citizenship doubts, Ms Campion then moved to the office of then-chief Nationals whip Damian Drum.

But the ministerial code of conduct makes it clear partners cannot be employed by any other minister without an explicit prime ministerial go-ahead.

Section 2.23 of the code states a minister's "close relatives and partners are not to be appointed to positions in their ministerial or electorate offices and must not be employed in the offices of other members of the executive government without the Prime Minister’s express approval".

Before question time, a spokesman for the prime minister's office dismissed claims of anything wrongdoing, saying "the Deputy Prime Minister did not breach the ministerial code of conduct because Ms Campion was not his partner at the time of the staff appointments."

The spokesman also said "the Prime Minister was not aware of the relationship" at the time of the appointments to the offices of Senator Canavan and Mr Drum.

Opposition Leader Bill Shorten asked Mr Turnbull in question time whether he still supported Mr Joyce, and whether Mr Joyce would be serving as acting prime minister when Mr Turnbull travels to the United States next week.

Mr Turnbull responded: "Yes in response to both questions."

It's understood that Mr Joyce and Ms Campion have only moved in together in recent weeks. She is not yet considered his designated "spouse" for the purposes of travel and entitlements.

Cabinet minister Nigel Scullion, who is leader of the Nationals in the Senate, was later asked about the definition and whether most Australians would consider Mr Joyce to be in a relationship with Ms Campion, given they are having a child.

"Oh look, absolutely," Senator Scullion told Sky News. "Absolutely there's no doubt about that."

Nationals' chief whip Michelle Landry said Mr Joyce's travails had been discussed during Monday's party room meeting.

"There was strong support for Barnaby to remain leader of the National Party," she said after the meeting. "Barnaby is a once in a generation politician, he has been fantastic for people in the bush."

Treasurer Scott Morrison said "Barnaby’s own private conduct, it's not for me to defend him on that. People know my views on these things, but I’m also very aware of human frailty," he told News Corp.