Julie Bishop says she could have beaten Bill Shorten in the May Federal election — had her colleagues made her prime minister in last year’s brutal leadership fight.

In an explosive interview with The Sunday Times Ms Bishop — who last week sensationally announced her retirement from politics at the May poll — said that not only did she believe she could have beaten Mr Shorten but Labor also feared she would defeat him.

Shedding more light on last year’s infamous August 24 leadership party room meeting in which Scott Morrison was picked to replace Malcolm Turnbull — after the ex-PM stood aside following a petition signed by a majority of Liberal MPs demanding a secret ballot to select a new leader — Ms Bishop accused her colleagues of pulling their support for her at the 11th hour.

She said before she entered that partyroom meeting there was a belief she had the support of at least 28 colleagues to become prime minister — more support than Mr Morrison.

Instead she got just 11 votes, which saw her knocked out in the first round of voting. Eventually, Mr Morrison defeated Peter Dutton 45 votes to 40.

Ms Bishop named Defence Minister Christopher Pyne — who on Saturday confirmed he would be not be contesting the next election — as a major player in a behind-the-scenes plot to stop her colleagues from voting for her.

She said she began ringing her colleagues on the afternoon of August 23, after it became clear Mr Turnbull would be replaced the following day.

“I had commitments from a number of people,” Ms Bishop said of her colleagues.

“When I say commitments, a number of people said ‘thank you for calling us. Yes we will support you’.

“I couldn’t understand why those who thought that they would support me, decided not to.

“I am now told that there was a view, led by Christopher Pyne and others, that even though I would have 28 votes — which was many more than Scott Morrison — it wouldn’t be enough to beat Peter Dutton.

“So, they wanted to make sure that happened,” she said.

“If I had known that was what their thinking was, I could have dissuaded them of it but also I would have pointed out that the question was: Who could beat Bill Shorten?

“And I was confident that I could (beat Shorten).

“And that was Labor’s thought too. I felt confident (of winning the leadership) after the assurances I had received over the phone.

“I rang everyone on that (August 23) Thursday afternoon.

“No one said to me that they weren’t voting for me because they didn’t think I could beat Bill Shorten. No one said that. There were 11 votes. Take out Malcolm and me — there were nine.

“For all the commentators to say ‘she could only get nine votes’, there were actually 28 who were going to back me but they were persuaded to back Scott Morrison.

“I knew the level of support Peter Dutton had, I knew the level of support I had. I knew the level of support Scott Morrison had.

“ Otherwise I wouldn’t have put up my hand.”

Ms Bishop said she had felt a “responsibility” to run for the leadership — particularly to women.

“Because I had been the party’s deputy leader (for 11 years), I felt a responsibility to put my name forward,” she said.

“And I also felt for all the women in Australia who had seen me as deputy for so long. I thought I’d be letting them down if I didn’t put my hand up.

“So, from that point of view it was a long shot because it was so late — Scott Morrison and Peter Dutton had been in the field for quite some time shoring up votes.”

After 20 years as the Federal member for Curtin, the hugely popular Ms Bishop has announced she will retire from politics at the May election.

Her decision is a huge blow for Mr Morrison who also has to deal with the political retirements of Mr Pyne, former defence industries minister Steve Ciobo, Jobs Minister Kelly O’Dwyer, Human Services Minister Michael Keenan and Indigenous Affairs Minister Nigel Scullion.

Ms Bishop resigned as the nation’s foreign affairs minister shortly after Mr Morrison was chosen as Australia’s 30th prime minister.

She says her decision to retire from politics was made just a few weeks ago.

Ms Bishop said that had Mr Turnbull still been PM, she would not have resigned as foreign affairs minister.

“I didn’t want to endorse what had happened and by continuing to accept what had happened I would have been endorsing it,” she says of her decision to quit as foreign affairs minister.

“And also, there had to be a level of trust with your Cabinet colleagues and I thought that had broken down and it would be better for them to have a new team and for me to step back.”

She says of Mr Turnbull’s demise: “We walked out of that partyroom meeting together.

“We went back to his office for a short moment and then I went back to see my staff.

“We were pragmatic about it. I think I indicated to him that I wouldn’t be staying in Cabinet.”

Ms Bishop remains loyal to Mr Turnbull.

“He compromised on a number of policies because of the pressure of some within the party, and yet they (Liberal MPs) were still not satisfied,” she said.

“He was concerned that whatever compromises he made he would never satisfy them until they got what they wanted.

“Ultimately, they wanted Peter Dutton as PM, but they didn’t get Peter Dutton as PM.”

Ms Bishop’s comments come on the eve of Mr Morrison’s first visit to WA this year — the west being a must-win State for the coalition if it is to hang on to power.

Some of the WA Federal MPs who did not vote for Ms Bishop, such as Christian Porter and Ken Wyatt, are now fighting for political survival.

Ms Bishop revealed some of her WA colleagues had contacted her since the August 24 vote to apologise for not voting for her.

She denied she was angry at her colleagues, saying she respected the party’s decision.

“There is nothing to forgive. They had a choice and they exercised their choice,” she said. “Everyone is responsible for their own decisions and their own action.

“We all have to take responsibility for what we do. It doesn’t matter now. The moment is gone.”

But she was less diplomatic about WA Liberal senator and powerbroker Mathias Cormann, who had played a critical role in Mr Turnbull’s demise by backing Mr Dutton as PM.

“I don’t understand his (Senator Cormann’s) motives in seeking to change the leadership to Peter Dutton last year,” Ms Bishop said.

“You still wish he would explain his motives in backing Peter Dutton over Malcolm Turnbull and causing enormous instability within the Liberal Party.

“He backed Peter Dutton who had very little support in WA and who fought against WA getting a better GST deal.

“Peter Dutton is on record as arguing against WA getting a better GST deal.”

Five people — including four women — have nominated for Curtin pre-selection.

Despite speculation Ms Bishop was supporting foreign affairs specialist Erin Watson-Lynn as her successor and the Cormann camp supporting former university chief Celia Hammond, Ms Bishop remained adamant she was “not backing anyone”.

“I really want to make this point — seriously make this point,” she said.

“ Sitting members should not be seeking to influence the lay members of the party on who they elect as their representative.

“That is a key tenet of a democratic organisation — that (lay) members of the Liberal Party have a right to choose their representative.

“I am not backing anyone. I am meeting with them (nominees) all.”

Ms Bishop also remained adamant she was not pushing for a woman to replace her in Curtin, although she said she was buoyed by the number of women who had shown an interest in the position.

“I didn’t say I want a woman (to be the Liberal candidate for Curtin,” she said. “I want the best person. I will back whoever the pre-selectors come up with.”

Despite never having become PM, Ms Bishop said she would leave politics with no regrets.

“I always aimed to be foreign minister and I achieved that,” she said.

“I am absolutely leaving on a high note.”

In terms of “unfinished business” Ms Bishop said justice for the families of the victims involved in the MH17 tragedy was top of the list.

“I most certainly would have liked to conclude the negotiations with Russia, but as long as they are resolved in a way that brings some kind of peace and finality to families then I am happy with that,” she said.

“It doesn’t have to be me (to conclude the negotiations).”

Ms Bishop says the negotiation of a maritime boundary treaty with Timor Leste was arguably her greatest achievement as foreign affairs minister.

But many say her handling of the MH17 crisis was her finest moment. She says the tragedy also provided her with her darkest moments.

Ms Bishop said seeing the remains of Australians airlifted in coffins from Ukraine to the Netherlands was an image she will never forget.

“I remember it all, moment by moment, as if it was yesterday,” she said. “I cannot imagine I would ever forget that. Unless you were actually there on the ground it’s hard to envisage what it was like.”

Looking ahead beyond politics, Ms Bishop says she is “excited about the future”.

“I’m in a very good place,” she said. “After 20 years in any role, it’s a challenge to leave but I’m excited by the future. I’ve had a number of very attractive offers for a post-political life. But I am not going to consider any until I cease being a member of parliament.

“I don’t cease being a member of parliament until the election is called. After that, I am private citizen Julie Bishop.”