The reason given for Scott Morrison’s secretive assumption of other ministers’ jobs makes no sense, an international expert in cabinet government says, as new testimony hints his power grab may have been even wider than imagined.

Mr Morrison’s assumption of cabinet authority is at the centre of an unfolding scandal, and even one of the previous government’s most senior ministers, Opposition Leader Peter Dutton, admitted he did not know whether he had unknowingly shared the job of defence minister with his former leader.

“Obviously, the prime minister – or the former prime minister – had his reasons, his logic for it but [it was] not a decision that I was a party to or was aware of,” he said.

Canberra was shocked by reports that Mr Morrison secretly had himself sworn-in to assume cabinet portfolios in finance and health and, later, energy at the peak of COVID, including reported cases where two ministers were never told.

After being excluded from the plan, Mr Dutton on Monday could point only to justifications in initial reporting revealing the extraordinary measures: Doubling up would ensure additional “checks and balances” in cabinet during the pandemic, when government powers and expenditure were high and the future was uncertain.

‘Complete excuses’

“Well, bulls–t,” said Patrick Weller, emeritus professor of politics at Griffith University, who wrote the book(s) on cabinet government.

“If it’s true, why was he the minister of health, finance and resources and not minister for the treasury or foreign affairs and everything else?”

Dr Weller added that the pandemic could not explain Mr Morrison’s assumption of the resources portfolio or the grounds on which he intervened in it: “This is all complete excuses.”

Disquiet grew in the Nationals on Monday as some MPs said the undeclared occupation of the energy portfolio by a Liberal prime minister was a violation of the Coalition agreement – the contract that splits portfolio responsibilities between the two parties, which is renewed each Parliament.

Mr Morrison apparently only declared that he had an undeclared joint role in charge of the resources portfolio when he told the cabinet minister, Nationals MP Keith Pitt, he did not have the authority to approve a controversial gas project.

In the party’s strongest statement on the matter yet, deputy leader Perin Davey told The New Daily the previous government had breached more than a governing agreement.

“Morrison appears to have rewritten the whole principle of a cabinet government,” she said.

One senior member of the previous government, who had been close to the PM said, on Monday that media reaction had been overblown.

“It would be remarkable if there weren’t contingencies during a global pandemic,” the Coalition insider said.

PM was twisting the rules

But Dr Weller said contingencies such as ministers falling sick would never have posed a problem and presented only minutes of immediate work.

He said Mr Morrison took the leeway afforded by democratic conventions to concentrate power in his hands to a degree that totally undermined the system of giving ministers legislative power so government could function.

“They’re twisting the notion of the constitutional rules,” he said.

“If you’re a departmental secretary, you have two ministers, both of whom have legal authority, to tell you what to do, telling you to do opposite things?

“That’s impossible.

“I would have thought that if you’re a minister with any backbone, and you discover the prime minister has been rustling around in your department making decisions which reverse the ones that you’ve made you either challenge him or you resign.”

The takeover also undermined, Dr Weller said, the obverse of ministerial powers – ministerial responsibility – two concepts at the very foundation of cabinet government.

The member for Cook offered only a glib reply to a journalist who asked him if he wished to reply to comments by PM Anthony Albanese that his actions had “trashed” the democratic process.

“Since leaving the job I haven’t engaged in any day-to-day politics,’’ the former PM reportedly texted.

Motivations unclear

Accounts for why Mr Morrison took such an idiosyncratic approach to cabinet collegiality have produced only more questions about the functioning of a government whose inner-workings seem to have surprised even those at its core.

In between the missing detail, Dr Weller sees the emerging portrait of a prime minister who coveted others’ responsibilities while seeming to disregard his own presiding powers and responsibility.

“I think I can actually say that he’s unique” he said.

“God knows what his motivations were.

“It’s a bizarre comment on the lack of skills of a prime minister to wield the powers of the prime minister: Rather than wield the powers, he chooses to circumvent them.

‘‘That’s a comment on his capacity as prime minister and his confidence.”

On Monday afternoon, a spokesman for Governor-General David Hurley confirmed Mr Morrison had held additional ministries.

It was reported on Monday that one of the most senior colleagues to share a portfolio with Mr Morrison, the then finance minister Mathias Cormann, was aware of the arrangement.