Once Mr Joyce was ruled ineligible by the High Court on October 27 he lost access to the entitlement, with the Nationals then forced to pick up the tab for byelection advertising and campaign material. Mr Joyce's work expenses are being audited by the Independent Parliamentary Expenses Authority in the wake of the scandal that ended his deputy prime ministership last week. Mr Joyce resigned after a fortnight of scrutiny over his extramarital affair with former media adviser Vikki Campion. The IPEA initiated the inquiry on February 7, when the news of Mr Joyce's affair - and claims of potential misuse of public funds - first broke. Mr Joyce has denied misusing any of his entitlements. "The audit is ongoing and IPEA is unable to provide a timeframe for its completion at this stage," the IPEA said. "In accordance with the IPEA Act 2017 an audit report may be published if IPEA considers it appropriate." Barnaby Joyce poses for a portrait in his New England electorate. Credit:Alex Ellinghausen

A spokesman for Mr Joyce said “all spending was within the printing and communications guidelines, complied with the necessary requirements and was independently approved prior to distribution”. Material distributed included an electorate-wide, community newsletter, several newspaper advertisements for a regular monthly column published in an agricultural supplement and a letter to all New England constituents outlining facts surrounding the discussion of Mr Joyce’s citizenship. “It was a matter of public record at the time that Mr Joyce sent a letter to each household after he requested his citizenship be referred to the High Court. In that letter he apologised to constituents for the inconvenience caused while the case was before the court,” the spokesman said. Maverick Nationals MP George Christensen spent more than any other politician on office consumables, publications and printing in the last three months of last year - costing taxpayers more than $111,000 in three months. More than $100,000 alone was spent on printing pamphlets.

Other big spenders on these entitlements included Liberal MP Stuart Robert ($110,000), Prime Minister Malcolm Turnbull ($109,000) and Liberal frontbencher Paul Fletcher ($106,000). Overall, parliamentary expenses cost taxpayers $25 million in the three months to December, with three quarters being spent on office facilities and administration.

Domestic travel was the next highest costing category, with taxpayers forking out $2.7 million between October and December for MPs to travel between Canberra, their homes and events around the country. Conservative senator Cory Bernardi charged taxpayers $1900 to travel to Sydney from Adelaide on September 16, the night before the launch of the "No" campaign for same-sex marriage he attended. His total domestic travel bill of $27,000 was higher than Environment Minister Josh Frydenberg.

On overseas travel, Nationals MP Keith Pitt and recently promoted Small Business Minister Craig Laundy spent more than $34,000 in three months on visits to the US, Canada, China and PNG, only $2000 less than now former immigration minister and now Home Affairs Minister Peter Dutton. Opposition Leader Bill Shorten's staff entitlement costs were the highest at nearly $600,000 - more than $100,000 more than Mr Turnbull's staff entitlements. Mr Shorten also charged more than any other MP for family travel, spending nearly $10,000. He was followed by crossbencher Bob Katter ($6500) and West Australian frontbencher Ken Wyatt ($6000). Mr Wyatt also spent the most on domestic airfares, at $55,000. Mr Katter was the biggest spender on car costs, at $44,000.