The Independent Parliamentary Expenses Authority (IPEA) has told Barnaby Joyce it can’t give him a finish date for the audit into his travel and related expenses, citing the difficulties of an aging system and consulting third parties.

The audit has been underway since early this year, sparked by the controversy around his affair with his former staffer and now partner Vikki Campion. Eventually the row around the affair, which was accompanied by allegations of sexual harassment, saw Joyce resign as Nationals leader and deputy prime minister.

On May 22 Joyce, who has answered multiple questions from the IPEA, wrote to the authority asking where the audit was up to.

The authority’s CEO Annwyn Godwin said in a reply dated May 24 that it was progressing matters “as quickly and with as little formality as a proper consideration of the issues allows”. She said the authority was aware of the outcome’s potential impact “on the reputation and credibility of all involved”.

The IPEA was working “with aging systems and this requires manual integration of a variety of different data sets and information sources,” she wrote.

“It is therefore important that care and attention is given to cross referencing and substantiating details where appropriate.

"This cross referencing may require sourcing additional information from third parties adding to the timeframes overall.

"Due to our current engagement with a number of third parties, and noting the members of the authority must consider and deliberate upon the audit findings, I am unable to give you a definitive date by which the audit will be complete.

"I can however assure you that I consider it in everyone’s best interests that the audit is finalised as soon as possible,” the letter said.

Joyce said in his reply that as an accountant, he understood the issues with audit process.

But he said that “an extenuated period of no conclusion” risked the audit possibly being branded a “fishing expedition”.

Joyce has said his expenses were done by members of his staff and then checked by him to avoid mistakes in claims.

The Nationals launched an inquiry into the sexual harassment allegation, but Joyce has not yet received an outcome on that, either.