Tony Abbott and Bronwyn Bishop only decided that she should resign from the speakership after they realised a significant number of government MPs would not support her in a no-confidence motion due to come before the Parliament, according to Liberal MPs.

The loss of any Coalition votes for Mrs Bishop on the floor of the House would have been interpreted as an insurrection against the authority of the Prime Minister.

Yet so serious had the discontent become that in an intense series of private phone conversations among themselves, a number of backbench MPs decided that they would refuse to vote for Mrs Bishop when a no-confidence motion, planned for next week, was moved against her.

The number of Liberals planning to abstain from a motion to be sponsored by crossbench MPs and supported by the opposition had reached about ten, according to MPs involved, and was growing as the scandal continued.

While Mrs Bishop would have survived on these numbers, the trend was one-way and the outcome was becoming increasingly uncertain.

Mr Abbott's decision to force her from the Speaker's chair on Sunday therefore averted a potential crisis for his own leadership - potentially the second such "near death" experience this year.

It could have seen the Prime Minister's hand-picked Speaker humiliated or even tipped out of the chair as a result of his not being able to command a simple majority on that question on the floor of the chamber where government is formed.

And the danger for Mr Abbott has not passed yet. In a reprise of the roiling backbench discontent which saw a spill motion supported by 39 MPs in February, Fairfax Media can reveal several Liberals are again pushing for material changes to the way the government is run, with the most common demand being no more "captain's picks".

Mr Abbott was informed of fracture in party discipline over the weekend, Liberal MPs said. "The situation was already spinning out of his control," said a Liberal speaking on background.

Mr Abbott sought to restore control by engineering Ms Bishop's resignation and announcing an inquiry into the system of parliamentary expenses, parliamentarians said.

But the anger at Mrs Bishop continues to burn inside the NSW Liberal Party and there is now a push to force her out of Parliament altogether.

"She's 74, she's a laughing stock with the public and she's about to discover that she has become persona non grata in the party," said a Liberal senator.

Ms Bishop would come under increasing pressure to make sure she did not stand for re-election to Parliament, her internal critics said.

This would present an opportunity to put a strong candidate into a plum Liberal seat, Mackellar.

Advising of Mrs Bishop's resignation late on Sunday, Mr Abbott raised eyebrows by simultaneously asserting that she had done the right thing by resigning, while also refusing to say what she had done wrong.

"I have a great deal of personal respect for Bronwyn Bishop, and without wanting to underplay the significance of some of the errors of judgment which she herself has conceded and apologised for, I think she has certainly done the right thing today," he said.

Asked if Mrs Bishop should have apologised earlier, he said: "I am just not going to sit in judgment of a friend and colleague like that ... Bronwyn's resignation today, will help to restore public respect, but as I have said repeatedly this afternoon this is not just about one person – it is about a system which notwithstanding reforms by the former government, notwithstanding reforms by this government, is obviously gravely in need of further reform and that is exactly what will happen as a result of the review that I have announced today."

One MP said the backbench mood remained "uneasy" with MPs determined to take back control of decisions that should never have been surrendered to the Prime Minister's Office.

Complainants say Mrs Bishop's politically costly descent into infamy was a long time in the making and is seen by unhappy Liberals as the inevitable result of one of Mr Abbott's earlier decision to foist her on his party upon winning the 2013 election.

"We should never have let this post be decided by anything but a party room vote," said one malcontent.

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