Former Nationals leader Warren Truss has also intervened in the saga, saying Mr Joyce's affair with former staffer Vikki Campion had damaged the Deputy Prime Minister's ability to lead and the issue needed to be resolved "constructively and quickly".

Late on Tuesday, some Nationals MPs were discussing whether to form a delegation that would approach the embattled Deputy Prime Minister and call on him to stand aside.

However, many are paralysed with doubt and aren't ready to move on Mr Joyce. Unlike the Labor and Liberal parties, Nationals MPs have traditionally shied away from cutting down leaders and have only done it once in their history.

Mr Joyce fought back on Tuesday, insisting he could survive the scandal that threatens his career and has derailed the government's start to the 2018 political year.

But he was hit by fresh questions after Fairfax Media revealed he charged taxpayers to spend 50 nights in Canberra when Parliament was not sitting in 2017 - more than any other cabinet minister.

Mr Vaile, who served as deputy prime minister under John Howard, told Fairfax Media the story was "now getting to the point where it is affecting the government".

He said Nationals MPs had a responsibility "to the national interest first, the government second and the party's interests third".

"They are the junior Coalition partner and part of the government of Australia. They need to deal with this. How they do it is up to them," Mr Vaile said. "They must resolve this."

Asked if Mr Joyce could survive, Mr Vaile said: "I don't know".

"The gift of the leadership is something those members of the Nationals vote on - it's in their gift to give it and take it away."

Discussions have already begun about who could become Nationals leader, with NSW MP Michael McCormack and Victorian MP Darren Chester named as frontrunners.

At a minimum, Mr Joyce will likely be urged to take leave so he does not serve as acting Prime Minister next week while Malcolm Turnbull is overseas.

As Mr Joyce faced a sustained opposition attack in Parliament for the second consecutive day, he attempted to reassert control over his personal-political crisis by making a terse verbal statement to reporters, followed shortly after by a printed statement. In both he publicly apologised to his wife Natalie, their daughters and to his new partner for the pain he has caused them.

Mr Joyce's extramarital affair with Ms Campion, who lived in Canberra throughout 2017 and is expecting the Deputy Prime Minister's child in mid-April, has been linked to the split from his wife.

Official expense records show Mr Joyce claimed $16,690 in travel allowance for out-of-session nights in the nation's capital between January 1 and September 30, 2017. That is substantially more than top government figures such as Treasurer Scott Morrison, Finance Minister Mathias Cormann and Foreign Minister Julie Bishop.

Mr Joyce was acting Prime Minister for 10 of those 50 nights. Under the rules, Mr Joyce was entitled to claim $276 per night for official business as Deputy Prime Minister and $565 per night as acting Prime Minister.

Mr Joyce's office blamed the high number of nights in Canberra on the fact regional Australian cities - such as Tamworth and Armidale in Mr Joyce's electorate - do not have permanent Commonwealth offices like capital cities.

"It should be expected that the Deputy Prime Minister would use the Canberra office more frequently than those ministers who have capital city bases," the spokesman said.

However, Mr Joyce opened two brand new offices in his electorate in 2015, costing taxpayers more than $670,000. He opened a new electorate office in Tenterfield ($305,148) and a dedicated ministerial office in Armidale ($365,748).

Mr Joyce's claim of 50 nights of travel allowance while in Canberra is more than any other minister of the Turnbull cabinet, and far more than any other minister of a similar level of seniority.

In comparison, Treasurer Scott Morrison claimed travel allowance for just 23 nights in Canberra in non-sitting weeks, including 11 consecutive nights in the lead up to the federal budget in May.

Mr Joyce also claimed for 62 sitting nights - meaning he spent a total of 112 days in Canberra, out of 272 days, in the period examined. Fairfax Media does not suggest any of the Deputy Prime Minister's claims were outside the rules that govern MPs entitlements.

Labor, which had initially treated Mr Joyce's marriage breakdown as a private matter, used Question Time to ramp up the pressure on Mr Joyce and directly link Mr Turnbull to his deputy's scandal.

Mr Turnbull and other senior Liberals have been at pains to distance themselves from the scandal, placing responsibility for Ms Campion's employment in several government offices squarely with Mr Joyce.

Nationals MPs have described the affair as "embarrassing" and "a distraction", while Liberal MPs are furious with the junior Coalition party and want a swift resolution. Even MPs who are close supporters of Mr Joyce are now questioning whether he will last until the end of the week.

Fellow Catholic conservative Cory Bernardi was scathing in his assessment of the crisis, telling Sky News that voters have a right to expect two things from politics.

"One is that the Australian people will not get screwed by their government and two, ministers will not screw their staff," the Australian Conservative senator said.

Mr Joyce also on Tuesday dismissed reports of an incident at a Canberra bar seven years ago as untrue and "peddled by the bitterest of political enemies". He denied the allegations.