Embattled federal Speaker Bronwyn Bishop has revealed a federal department is examining two more charter flights she has admitted could have been used to attend party political events.

The development comes as Fairfax Media can reveal that Mrs Bishop charged taxpayers almost $1000 a day to travel in luxurious private limousines during her $90,000 fortnight in Europe.

The Speaker finally conceded on Saturday that she made an "error of judgment" when she chartered a $5227 helicopter to make the short journey from Melbourne to Geelong for a Liberal Party fundraiser last year.

Mrs Bishop refused to say sorry to the Australian taxpayer over the episode, saying her refund was apology enough. Despite admitting the only reason she travelled to Victoria on November 5 last year was for the party event at a golf club, she dismissed any suggestion she would resign her position as head of the federal Parliament.

"One doesn't resign for an error of judgment that is within the guidelines," she said.

Mrs Bishop revealed she had also asked the Department of Finance to look into two other charter flights she had taken since becoming Speaker – one to Young and one to Nowra – for the sake of "completeness".

"There were certainly public meetings, there could have been a fundraiser as well," she said.

But the charters are far from the only extravagance in Mrs Bishop's expense reports.

Fairfax Media can reveal the Speaker racked up a $14,000 limo bill in a little over a fortnight during her European trip in October.

On the same trip, Mrs Bishop's four fellow delegates spent between $1200 and $2800 each on ground transport. They typically travelled by public transport or in more modest embassy-arranged cars.

"There was a black BMW carting her around like royalty," said a source involved with the trip. "She wasn't about to take her eight-inch heels on the subway."

The Speaker's chief of staff and spokesman Damien Jones, who was on the trip with another staff member, confirmed the spending on Saturday.

"All presiding officers get their own transport," he told Fairfax Media. "In fact I think any head of delegations gets their own transport. So yes, that accounts for the $14,000."

Mrs Bishop and her staff also spent $42,000 on flights and $25,000 on meals and accommodation. The other parliamentarians – the Coalition's Nola Marino and Cory Bernardi​, and Labor's Glenn Sterle​ and Tony Zappia​ – each spent a fraction of those amounts.

The trip was partly aimed at securing Mrs Bishop a plum new job. She was running for president of the Inter-Parliamentary Union, a democracy group based in Switzerland. She lost the vote to Bangladesh's candidate.

Reminded the Treasurer had said the helicopter charter "failed the sniff test", Mrs Bishop said: "Joe [Hockey] says some funny thing sometimes, doesn't he? I think he said poor people don't drive cars or something."

Prime Minister Tony Abbott was standing by his hand-picked Speaker on Saturday. In his first public comments on the expenses scandal, Mr Abbott said he would not ask her to step down.

"No. She's repaid the money and she does a good job," Mr Abbott told reporters in Queensland.

"Bronwyn admitted it was probably an error of judgement and she's repaid the money. She has my confidence."

Mrs Bishop repaid the $5227 cost of the charter – plus a $1300 penalty – amid intense political and public pressure on Thursday.

Mr Abbott dismissed a suggestion she should stand aside as the department conducts its audit. "I don't think it's appropriate to stand aside simply because the finance department might be having a look at something."

He also dismissed suggestions that Mrs Bishop was being treated differently to former speaker Peter Slipper, who faced criminal charges over his expenses.

Labor has called on the Australian Federal Police to investigate the Bronwyn Bishop expenses scandal without further delay, saying the Department of Finance's internal audit should not stand in the way of a criminal inquiry.

Opposition waste-watch spokesman Pat Conroy has has written to the AFP for a second time, urging it to probe the chopper episode. The AFP has referred the matter to the finance department under what is known as the Minchin protocol​, which allows the department to conduct an audit to determine whether allegations are credible. If it decides there has been serious and deliberate wrongdoing it can refer the case back to the police.

But Labor believes the protocols do not apply if allegations are referred directly to the AFP.

"Refusing to investigate the allegations against Mrs Bishop would be inconsistent with the approach taken in the Slipper case," Mr Conroy said. "In any event, the Minchin protocol is no impediment to a police investigation into Mrs Bishop's conduct."

Labor believes the case hinges on whether Mrs Bishop signed a Presiding Officer's Charter Certification form. The form requires the Speaker to confirm that a charter is for her "office holder duties" and states that knowingly giving false or misleading information is a serious criminal offence.