Mr Duncan told Speaker Vicki Dunne that taxpayers' money should not be used for staff member Danielle Young to travel with Ms Jones, Mrs Dunne and Mrs Dunne's husband.

He said no such travel had ever occurred in any Australian parliament, and it was all the more unjustified in light of plans to abolish the study travel allowance.

Allowing Mrs Young to travel on public funds would be a new frontier, he said, warning that taking the adviser would attract immense scrutiny and criticism from the government, the media and the public, and should not be approved.

But Mrs Dunne rejected the advice and approved Mrs Young's travel, telling Mr Duncan that Labor backbencher and Deputy Speaker Mary Porter agreed with her decision.

''I don't believe I have the discression [sic] to not approve because it is unprecedented, or it doesn't happen elsewhere, or it may be commented upon,” Mrs Dunne wrote back.

Also on Thursday, it emerged that Mrs Dunne will take her husband, Lyle Dunne, to Samoa in July for a meeting of clerks and presiding officers at the cost of his airfare of $2800, despite the Remuneration Tribunal decision last month to abolish all study travel and all spouse travel immediately. Mr Dunne's travel was approved before the allowance was scrapped.

The Clerk's advice on staff travel was revealed on Thursday after a freedom of information request from this newspaper. The release prompted Ms Jones to hit back at Mr Duncan, claiming he had reversed his earlier advice.

''In a meeting in my office late last year the Clerk … said there would be no issue with approval if the criteria in the member's guide were met,'' she wrote in a letter to Deputy Clerk Max Kiermaier, who handled the FOI request. ''The advice to the Speaker is a strange reversal of the previous advice given to me.''

Mrs Young and Ms Jones visited Sweden and Korea at the end of last month. They were joined for part of the trip by Mrs Dunne and her husband, who visited Paris and Stockholm, and went on to London for a Commonwealth Parliamentary Association meeting.

Final costs are not in, but the staff member's trip was estimated to cost $9000, the two Assembly members' trips a similar amount and Mr Dunne's trip $7700, for a total of $33,700.

Mr Duncan wrote to Mrs Dunne on February 21 telling her the travel should not be approved. In 2011, then Speaker Shane Rattenbury (Greens) changed the guidelines to allow staff travel, and since then staff have travelled with politicians in Australia, but never overseas. Mr Duncan told Mrs Dunne it had never happened in other jurisdictions. In some, even MPs were not allowed to take overseas study trips. The Commonwealth had recently removed the entitlement for MPs, and staff had never been allowed.

Allowing Mrs Young to travel would probably be criticised, especially in light of the significant cost. He also pointed out that the Remuneration Tribunal had clearly signalled plans to reduce or abolish the allowance.

Last month, after news of the prostitution study tour became public, the tribunal brought forward its decision and abolished the allowance immediately.

Mrs Dunne defended her decision to allow the travel on Thursday, saying she had consulted Mrs Porter. The travel had been allowed by the guidelines and was in line with advice from the Remuneration Tribunal. She disagreed with Mr Duncan's reasoning that she ''should not approve it because someone might comment on it or because it had not been done before''.

Ms Jones said it was vital that the staff member, as her senior adviser, was on top of all of the outcomes of the meetings overseas, and it was of great benefit to have her help in co-ordinating and taking the minutes of meetings. Taking a staff member was better value than taking a spouse.