Former Liberal prime minister Malcolm Turnbull has called on Angus Taylor to resign from shadow cabinet and officially step forward to challenge Sussan Ley's leadership of the party, as rumours of a spill continue to grow.

Murmurs of a challenge to Ley's position have grown in recent days, despite the Coalition successfully re-forming last weekend.

Taylor, the current shadow defence spokesperson and former shadow treasurer, has emerged as the frontrunner to replace Ley in the event of a spill after fellow conservative Andrew Hastie withdrew from contention late last month.

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With the current parliamentary sitting week the last for the month, there is speculation a spill could be called in the next three days.

The Liberals held a partyroom meeting this morning, but with senators missing the meeting due to estimates sittings, a spill was not called.

However, Turnbull, who resigned from the frontbench in 2015 to successfully challenge then-prime minister Tony Abbott for the Liberal leadership, called on Taylor to do the same this week.

"I do think he should [challenge]", Turnbull said in a press conference at the Senate courtyard, where he issued his challenge to Abbott.

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"I think it is important to stand up and be counted.

"This is a place where you vote in public, so if Angus wants to be leader of the Liberal Party, he should stand up and say so, and say why."

Ley's position has become less secure as the Liberal Party flounders in the polls.

The latest Newspoll released on Monday saw the Coalition's primary vote slide to 18 per cent, now behind Labor at 33 per cent and One Nation on 27 per cent.

The Liberal primary vote is just 15 per cent.

Turnbull didn't say Ley – who has been opposition leader for less than a year – had been denied a fair go, saying it was part and parcel of politics.

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He admitted it was difficult to see a viable road back for the party.

"I sympathise with all of my former colleagues, but they are in a terrible state," he said.

"This is the Liberal Party facing an existential crisis.

"It's a long road ahead… they should be worried, these polls are terrible." 

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