British Foreign Secretary Liz Truss' assertion that China might use a Russian "invasion" of Ukraine as an opportunity to launch aggression of its own in the Indo-Pacific has sparked debate in Australia, with a former prime minister calling Truss' remarks "nothing short of demented".

Leading the criticism, Paul Keating, in a weekend op-ed for Pearls and Irritations, said her remarks after a bilateral security and defense meeting were "not simply irrational, demented".

Keating also suggested Truss go "back to her collapsing, disreputable government".

Keating served as Australia's Labor Prime Minister from 1991 to 1996 and said Truss's comments amplified the Australian government's "desperate promotion of Britain as a strategic partner of Australia in a policy of containment of China".

"The reality is Britain does not add up to a row of beans when it comes to East Asia," he said.

He wrote: "Britain took its main battle fleet out of east Asia in 1904 and finally packed it in with its 'East of Suez' policy in the 1970s. And it has never been back.

"Britain suffers delusions of grandeur and relevance deprivation. But there they were at Admiralty House kidding the rest of us that their 'co-operation' added up to some viable policy."