Senior ministers billed taxpayers tens of thousands of dollars for flights on Royal Australian Air Force planes in the week following last year's Liberal leadership spill.

Key points: Liberal MPs dumped Malcolm Turnbull in August 2018, prompting a change in the ministry

Liberal MPs dumped Malcolm Turnbull in August 2018, prompting a change in the ministry Peter Dutton and Mathias Cormann booked defence jets to get to swearing-in ceremonies

Peter Dutton and Mathias Cormann booked defence jets to get to swearing-in ceremonies The flights cost more than $60,000 in fuel, landing fees and airport handling charges

The flights, costing more than $60,000, were booked so Home Affairs Minister Peter Dutton and Finance Minister Mathias Cormann could attend swearing-in ceremonies.

Both resigned from the ministry the previous week after declaring they no longer supported Malcolm Turnbull.

And both flew on routes heavily serviced by commercial airlines, contrary to official guidelines.

Mr Dutton flew from the Amberley RAAF base near Brisbane to Canberra on the Sunday following the spill.

He was sworn in again as Home Affairs Minister on the Monday, then flew to the Gold Coast later that day.

The flights cost $25,396 in total, including the trips with no passengers to fetch the CL604 Challenger aircraft from, and return it to, Canberra.

He declined to comment on Wednesday, but said at the time "the swearing-in today will allow me to travel to the Gold Coast to attend the Five Country Ministerial meeting".

Treasurer Josh Frydenberg represented new PM Scott Morrison at the ceremony.

Peter Dutton alongside Governor-General Peter Cosgrove and Josh Frydenberg on the Monday following the spill. ( ABC News: Andy Kennedy )

The Five Country Ministerial meeting involves security and immigration ministers from Australia, Canada, New Zealand, the United Kingdom, and the United States.

The remainder of Mr Morrison's ministry was sworn in on the Tuesday, including Senator Cormann.

The ceremony was followed by the first meeting of Mr Morrison's cabinet.

Senator Cormann's flight from Perth to Canberra on the Monday cost $1,823.

After being sworn in, he flew back to Perth on a CL604 Challenger. Sending the aircraft to Perth and back to Canberra cost $37,720.

He held a press conference in Perth the following day.

A spokesperson for Senator Cormann said the role of defence jets was to allow ministers to meet commitments associated with their official, parliamentary or political responsibilities, and the cost of travel was higher for MPs from Perth.

"In the context of the high frequency of necessary work-related travel from Perth to Canberra, Sydney and Melbourne and back, Senator Cormann is an infrequent user of the special purpose aircraft — and only if that use is appropriate in the circumstances.

"On 28 August 2018 Senator Cormann was required both in Canberra and back in Perth later that day.

Senator Mathias Cormann was sworn in on the Tuesday following the spill. ( ABC News: Marco Catalano )

"Inevitably that travel from Canberra to Perth is more expensive than travel to locations on the East Coast.

"Two senior staff also travelled with the Minister on this occasion to facilitate dealing with office work on the five-hour trip back from Canberra to Perth that day."

In circumstances where commercial alternatives are readily available, guidelines state that defence jets may not be used.

Senator Cormann's spokesman said no commercial flight options were available "to accommodate all these commitments" and the use of the jets was approved "in the appropriate way".

Costs for defence jets are made up of fuel, landing fees and airport handling charges.

Guidelines state the CL604 Challenger aircraft must not be used when commercial flights are available. ( Royal Australian Air Force )

The entitlements system for politicians was overhauled in the wake of Bronwyn Bishop's "Choppergate" scandal, and MPs must now be prepared to publicly justify their use of public resources.

Senator Cormann has previously booked flights costing $37,000 so he could spruik the Government's personal tax cuts and lobby crossbenchers for its corporate tax plan.

Malcolm Turnbull's flight from Canberra to Sydney on the Sunday following the spill — his final chartered defence flight — cost $2,300.