A by-election loss for the Gillard Labor Government need not lead to Tony Abbott becoming Prime Minister.
Gillard has the support of 76 members of the House of Representatives while Abbott has the support of 74 (counting Tony Crook). With one Labor MP as Speaker, this turns into a 75-74 vote on confidence motions on the floor of the House – assuming that both Tony Crook and Bob Katter vote with Coalition MPs against Gillard
A by-election loss for the Gillard Government would lead to a 74-75 split on the floor of the house in favour of Abbott. But it is highly likely Labor MP Harry Jenkins would resign the speakership to prevent Abbott becoming Prime Minister.
What happens then? The Constitution (s.35) would appear to require the House to elect a new Speaker.
35. The House of Representatives shall, before proceeding to the despatch of any other business, choose a member to be the Speaker of the House, and as often as the office of Speaker becomes vacant the House shall again choose a member to be the Speaker. The Speaker shall cease to hold his office if he ceases to be a member. He may be removed from office by a vote of the House, or he may resign his office or his seat by writing addressed to the Governor-General.
However, it’s unclear what happens if no MP is willing to become Speaker. Ultimately there may be a new election – although it’s unclear what would happen if the Prime Minister didn’t recommend holding one to the Governor General.
In practise, both Labor and the Coalition would negotiate to win an additional cross-bencher’s vote. It’s hard to see any Labor-supporting crossbencher supporting Abbott, and it seems unlike that Bob Katter or Tony Crook would support Gillard (although the WA Nationals might support Gillard in return for concessions).
A by-election win for the Coalition would not automatically lead to Tony Abbott becoming Prime Minister. It would likely lead to further negotiations between the major parties and the crossbenchers – probably focussing on Tony Crook and Andrew Wilkie.
Gillard would likely survive a by-election loss as Prime Minister unless (i) Abbott could convince an additional MP to support him, or (ii) the House is unable to elect a Speaker and a fresh election is held. A fresh election would likely lead to a majority government – led by Gillard or Abbott.