The Independent newspaper reported Truss had opted for the private flight for her trip last week due to security concerns, although commercial flights were available.

The newspaper said she had travelled on the private government Airbus A321, which a senior source told them would have cost 500,000 pounds to operate.

The Foreign Office said the trip was within the rules set by the ministerial code, and using the private jet allowed the trip's delegation to travel together and have private discussions on sensitive security matters.

The department said commercial flights were fully booked, and that using a commercial flight would have separated Truss from her delegation and protection team.

They added using the private jet also gave Truss flexibility to return to the United Kingdom early if needed.

But UK Labour's deputy leader Angela Rayner said the use of the private jet showed "the public exactly quite how little respect this Conservative government has for taxpayers' money".

"It is obscene that government ministers are jet setting yet are hiking taxes and refusing to do anything to help working families when they are feeling the pinch of the cost of living crisis," Rayner said.

"Tories waste disgusting amounts of public money on their own vanity and comfort, Labour wants to see families see a cut to energy bills, that is the difference."

Scottish National Party environment spokeswoman Deidre Brock added that it was a "grotesque misuse of taxpayers' money to fund her jet-set lifestyle".

Brock added: "With a record like this, Lavish Liz will make a fitting successor to Boris Johnson."

In a policy paper called Back to Black which Truss co-authored in 2009 she, along with others, outlined how "every public sector worker should feel personal responsibility for the money they spend and the money they save.

"They should spend taxpayers' money with at least the care they would give to their own.

"This change of mindset would be reflected in everyday changes such as travelling by economy rather than business class, to larger scale changes around focusing on value for money."

The UK ministerial code says that ministers can authorise non-scheduled flights "when a scheduled service is not available, or when it is essential to travel by air, but the requirements of official or parliamentary business or security considerations preclude the journey being made by a scheduled service".

Labour MP Chris Bryant tweeted: "For comparison, my first trip as a foreign office minister was on easyJet at 6am and we didn't pay for speedy boarding."

"It's necessary for the Foreign Secretary to travel abroad to pursue UK interests around security, trade and technology, as she did during this visit to Australia," a UK Foreign Office spokesperson said.

"Travelling this way allows ministers to have private discussions on sensitive security matters and flexibility to respond to rapidly changing global events.

"This trip used government transport and was fully within rules."

The Foreign Office said all information on the trip would be set out in regular transparency data.

Australian Associated Press