Her much-publicised relinquishing of the high-profile cabinet role in early 2017 due to a Gold Coast apartment purchase when in the area on government business has been recounted in Mr Turnbull's book, A Bigger Picture.

The former Prime Minister, who counted Ms Ley as a friend before claiming their relationship soured, put the almost daily release of her travel details down to the work of a former staff member.

"It was a classic hit job," Mr Turnbull wrote.

"It appeared a disgruntled ex-staffer had initially made the claims to (reporter) Annika Smethurst of the Courier Mail and then further research through her travel claims did the rest.

"Sussan's initial explanation that the apartment purchase was unplanned and 'spur of the moment' wasn't credible and was quickly discredited.

"I begged her not to say any more to the media until she'd done all her homework.

"But day after day there were bad headlines calling for her to resign or be sacked.

"Her colleagues rallied around to put the boot in - anonymously of course."

But Mr Turnbull's understanding of who was responsible for the "hit job" is at odds with a recent New Daily website article which put the blame at the feet of a Labor Party dirt unit.

"The real story was that Ley was sick and had cancelled her appearance and trip to the Gold Coast. At the last minute, Prime Minister Malcolm Turnbull's office had intervened and insisted she attend, necessitating the chartering of a RAAF flight to transport the virus-ridden Ley to the conference," the website reported.

"The irony was not lost on Ley's office when the $12,000 charter flight exploded into a crisis.

"Turnbull had remained furious with Ley after the 'Mediscare' campaign during the 2016 election and she was out of favour.

"The fact that she and her office had repeatedly begged to respond to Labor's claims, compiling huge dossiers of material - only to be rebuffed by Turnbull's team and even his pollster Mark Textor - didn't seem to matter."

Travel claims were a hot topic at the time with another Liberal high-profile casualty being Bronwyn Bishop due to "Choppergate" two years earlier.

"Various claims of expenses abuse were levied at other ministers, including Industry, Innovation and Science Minister Greg Hunt, who'd used the family reunion entitlement to take his family on a trip to Noosa while he was notionally at least working on the Sunshine Coast," Mr Turnbull wrote.

"I was sorry to lose Sussan.

"She was a friend as well as a good colleague who shared my liberal values.

"Sadly, however she became bitter about having had to resign.

"By August 2018, frustrated because she hadn't yet been reinstated to cabinet, she threw her lot in with Peter Dutton on the basis that he'd promote her."

A subsequent investigation conducted by the finance department concluded Ms Ley had made only one breach of travel entitlements for a five-minute trip to attend the Gold Coast apartment auction in May.

Ms Ley, who has been returned to the ministry with the environment portfolio following her success in last year's federal election, said she had moved on from the saga.

"I have been told it was a hit by Labor, now I'm being told it was by others," she said.

"Frankly I think people are tired of politicians focusing on old feuds and bruised egos, instead of the vastly more important issues affecting our communities right now.

"The matter was independently reviewed, and I have moved on."

Mr Turnbull also explained his decision not to fight back on "Mediscare".

"There was a great deal of criticism that we hadn't spent more time and money attacking (Labor leader Bill Shorten) and expressly refuting the Mediscare campaign," he wrote.

"Looking back, and instinctively, I think this is probably right, but the reasons for staying - largely - positive were compelling.

"We had very little money.

"Labor outspent us by millions and had I not contributed $1.75 million to the campaign myself, we'd have almost certainly lost.

IN OTHER NEWS:

"In a crowded and confused free media environment - made all the more crazy by fake news on social media - the only way to be sure to get your message across is with paid advertising and that costs a lot of money."

Mr Turnbull also briefly recounted in his book the demise of another Liberal Sophie Mirabella, who lost the seat of Indi to Cathy McGowan in 2013 and retired from politics following her loss three years later.

"I've observed that if a member offends enough of their constituents for long enough, they can lose the safest seat," he wrote.

"That's how Sophie Mirabella lost the seat of Indi to independent Cathy McGowan in 2013, and incredibly the Liberal Party ran Mirabella again in 2016 when Cathy, predictably, won with an even bigger majority."

Mr Turnbull needed the backing of Ms McGowan and other cross-benchers to support the government on motions of confidence and supply after the 2016 election.

"Cathy McGowan and Bek Sharkie were quick to give me those assurances as indeed was Bob Katter," he said.

"Although, shortly after announcing his agreement, he added that he could change his mind at a moment's notice."