Defence spending boost critical ahead of AUKUS, former ASIO boss Duncan Lewis warns

ASIO's former top official Duncan Lewis has underscored the great financial challenge the incoming and future federal governments will face in the wake of Saturday's election results.

Mr Lewis, who was also previously the Defence Department's secretary and an ambassador to the European Union, said ministers needed to consider raising defence spending well beyond the promised floor of 2 per cent of GDP pledged by Labor in the lead-up to the election.

The federal government signed an historic trilateral agreement in September last year with the US and the UK resulting in the delivery of at least eight nuclear-powered submarines to be ready by the late 2030s.

While Mr Lewis welcomed the AUKUS deal as a "game changer", he said he regretted the decision had been made 20 years too late.

"I have a concern that we have bought nothing much that goes 'bang' for many, many years in the defence capability portfolio," Mr Lewis said on an episode of the Australian National University's National Security Podcast released on Thursday.

"I carry responsibility for some of that as a former secretary of the department, but we urgently need to buy things which will give us a symmetric advantage very quickly.

"If we think that 2 per cent or 3 per cent of GDP is going to pay for nuclear-powered boats and for the defence capability that I believe we are going to require in the not-too-distant future, we're kidding ourselves."

Prime Minister Anthony Albanese promised an elected Labor government would set a minimum defence spending floor of 2 per cent of GDP and review struggling, and often costly, military projects failing to hit targets.

But Mr Albanese did not outline specific acquisitions Labor would look to until it could consult in government. Its defence minister is expected to be announced next Wednesday.

Shortly before the federal election was called, former defence minister Peter Dutton said the multibillion-dollar AUKUS deal for nuclear submarines was being fast-tracked, with designs expected within months.

Mr Lewis said the government needed to look to boosting defence capability with more immediacy in the intervening years, given the fast-shifting nature of the situation in the Indo-Pacific region.

"No longer can we afford to have these massive missteps of equipment, you know, the capability procurement failures," he said.

"You think back to issues like the Seasprite helicopter [which] was very expensive - let's call it a blunder. To pay the French $5.5 billion for a submarine ... not delivered.

"We can't afford to have these sorts of distractions from the Defence dollar ... all the Defence dollars need to be going to providing an effect."

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In the years since Mr Lewis stepped down from his role as ASIO's director-general, China has played a more assertive role in the region.

But the former top diplomat, quoting former US president Teddy Roosevelt, said political shirt-fronting was likely not the best way forward.

"One should talk softly but carry a big stick, and you'll go far," he said.

"And my concern in the last few years has been that we have been rather louder than we should have been."