Liz Truss has responded after Labour accused the foreign secretary of spending "disgusting amounts of public money" on her own "vanity and comfort" by using the government's private jet for her trip to Australia.
The flight on the private government Airbus A321 taken last week was opted for due to security concerns, and the Independent reported is estimated to have cost £500,000.
The Foreign Office said the trip was within the rules set out by the ministerial code and that using the chartered plane allowed Ms Truss and her delegation to have "private discussions on sensitive security matters".
And Ms Truss later defended her decision to use "the government plane", telling reporters it enabled her to "do the work overseas which is ultimately delivering for the British people".
"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," Ms 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."
Labour chairman of the Commons Committee on Standards, Chris Bryant, added in a tweet: "For comparison, my first trip as a Foreign Office minister was on easyJet at 6am and we didn't pay for speedy boarding."
Meanwhile, the SNP's spokesperson for the environment, Deidre Brock, said chartering a private jet to Australia would constitute "a grotesque misuse of taxpayers' money to fund her jet-set lifestyle".
"With a record like this, 'Lavish Liz' will make a fitting successor to Boris Johnson," she said.
The 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".
Approached on the claim, the Foreign Office said commercial flights to Australia at the time Ms Truss was travelling were fully booked and that using a standard commercial flight would have separated the foreign secretary from her protection team.
They said the private jet also gave Ms Truss the flexibility to return to the UK at pace if needed.
"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 spokesperson for the department 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."
Speaking to reporters, Ms Truss said: "I used the government plane. That is why we have a government plane - to enable government ministers to conduct government business. And that is what I flew to Australia in."
Asked whether it was good use of taxpayers' money and if it would not have been better to fly in a commercial plane, the foreign secretary continued: "Well we have a government plane precisely so that government ministers can travel.
"Well every government decision is based on value for money. We have a government plane specifically so ministers, like me in my role as foreign secretary, can go and do the work overseas which is ultimately delivering for the British people."
The Airbus A321, which Ms Truss had used for her trip, can only be used by the government.
The Foreign Office added that all information on the trip would be set out in regular transparency data.
Ms Truss co-authored a policy paper called Back to Black in 2009 where she and 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."