He played himself into the middle of the leadership crisis last week when he declared his support for the prime minister was "not unconditional". "Comrade, ask me next week," was his memorable reply when asked if Mr Abbott's leadership would survive. Backbench influence: Senator Arthur Sinodinos. Credit:Christopher Pearce On Sunday, he went further and declared he would vote in favour of Monday's spill motion, revealing frustration at Mr Abbott's move to circumvent discussion among MPs by bringing the party-room meeting forward by 24 hours to 9am Monday. "I am disappointed the party-room meeting has been brought forward. MPs should be given adequate time to discuss the matter at hand," he said. Senator Sinodinos' intervention has been dismissed by some backers of Mr Abbott as motivated by revenge after he was forced to resign from the ministry in December and the announcement leaked ahead of time.

But senior party colleagues insisted on Sunday that he is wise enough to separate any resentment at the handling of his resignation by the prime minister's office from his legitimate misgivings about the direction of the government. They said his resignation had freed him from the cabinet solidarity that has locked down other senior Liberals from airing grievances and his support for a spill represents the seriousness of discontent with the current leadership. "Arthur is not the type of bloke who straps on a bomb vest and goes out and blows himself up. His position will be very considered and carefully calibrated," said a source. Another Liberal said: "He knows how good government works, he was there under Howard. For that reason he has given backbenchers plenty to think about in supporting a spill." Senator Sinodinos decided to walk the plank after the Independent Commission Against Corruption's findings against the Eddie Obeid-linked Australian Water Holdings – a company once chaired by Senator Sinodinos – were delayed until at least March this year.

Loading He insisted throughout the inquiry and when he resigned that he ICAC would eventually clear him of any corruption finding. In December, Senator Sinodinos said the leaking of his resignation announcement "did not assist the orderly workings of government" in a thinly-veiled swipe at the prime minister's office, led by chief of staff Peta Credlin.