Julie Bishop says there remain conflicting views about whether Malcolm Turnbull offered Peter Dutton the role of deputy Liberal leader after the first bitter leadership spill last year.

Mr Dutton said he put his hand up for the leadership in August because he believed he could win the election, which was then about nine months away.

After speculation he had lost the confidence of multiple cabinet ministers, Mr Turnbull called a leadership spill on the Tuesday morning, beating sole challenger Mr Dutton 48-35.

“He offered me the deputy leader position,” Mr Dutton told Sky News in a documentary that will screen on Tuesday night that delves into the bitter battle.

“I said to him, given what had just taken place, that wasn’t credible. It wasn’t his to gift either.”

Mr Turnbull denies offering Mr Dutton the role, which was held by the then foreign minister Julie Bishop.

Ms Bishop, who declined to be interviewed by Sky for the program, said in Brisbane on Tuesday she was unaware of the discussion between Mr Turnbull and Mr Dutton.

“There’s obviously a conflict over the version of events,” she said.

“But everyone knows you can only achieve the deputy leadership of the Liberal party by a ballot of the party room.”

A second leadership ballot occurred days later after Mr Dutton was able to get a majority of Liberal MPs to sign a petition calling for a challenge.

Mr Turnbull didn’t fight for his role but instead chose to quit parliament, leaving Mr Dutton, Ms Bishop and Scott Morrison to fight it out for the leadership.

The documentary reveals a dinner conversation between Queensland Coalition MP Luke Howarth and former NSW Coalition MP Craig Laundy might have been the catalyst for the leadership challenges.

Mr Howarth told his colleague at the start of the divisive week he planned to tell Mr Turnbull to resign as leader at the next election.

“I was going to be very clear and maybe suggest that him and Tony Abbott might want to retire at the next election and let new leadership come through,” he told Sky News.

“I was thinking of the party and thinking that perhaps it’s time for new leadership.”

The “heated conversation” rang alarm bells for Mr Laundy, who immediately spoke to his ally, Mr Turnbull.

“I rang Malcolm and … I explained the nature of the heated conversation, the disagreement, the anger and the passion that Luke had,” Mr Laundy said.

“I had a genuine concern that he could stand up the next day and say or do something that would be bad news.”

Mr Laundy let Mr Howarth know he didn’t think Mr Dutton would be a positive change for the Liberals.

“As much as Duts is a mate of mine, can you imagine how electorally popular he would be in NSW, Victoria and South Australia?”

Despite coming out on top at the end of the bitter week, now Prime Minister Scott Morrison said he thought Mr Turnbull could have led the Liberals to victory at the election.

“That was certainly my view,” he said.

– AAP