Scott Morrison was sworn into a fourth portfolio, with documents revealing more about the former prime minister’s moves to secretly install himself across his government’s ministries.

It came as Mr Morrison emerged on Tuesday to defend his actions.

“We had to take extraordinary measures to put safeguards in place [as the pandemic hit],” he told Sydney radio 2GB, of the health and finance portfolios.

“They were there as a safeguard, as a redundancy because the powers in those portfolios weren’t overseen by cabinet. The minister himself, and in both cases, had powers that few, if any, ministers in our federation’s history, were having.”

It follows the emergence on Tuesday of an administrative arrangements order for the social services portfolio, signed by Mr Morrison and Governor-General David Hurley on June 28, 2021. It is on top of the former PM also being privately sworn in as health minister, finance minister and resources minister.

Former health minister Greg Hunt knew of the arrangement in his portfolio, but former finance minister Mathias Cormann learned of it only at the weekend, when the revelations emerged.

Mr Morrison said he had called Mr Cormann, the former leader of the government in the Senate to apologise.

“That was an error and an oversight and I’ve apologised,” he told 2GB radio.

Mr Morrison said it was “not his recollection” that he had been secretly sworn into any other portfolios – although he was checking.

“I’m pursuing that, but not to my recollection. There were a number [of others] that we considered at the time to safeguard,” he said.

Earlier, Prime Minister Anthony Albanese declined to directly express his support for the Governor-General on Tuesday morning, as the Department of Prime Minister and Cabinet inquires into the legality of Mr Morrison’s leadership arrangements.

“The Governor-General acted on the advice of the government of the day. It is Scott Morrison that initiated this extraordinary and unprecedented action,” Mr Albanese told the ABC.

“The Governor-General’s job is to take the advice of the government of the day. I dont intend to pass judgment … blame for this lands squarely on the former government.

“Clearly other ministers knew … they chose not to make it public.”

Mr Albanese indicated there could be further portfolios Mr Morrison swore himself into.

“There may well be more but I’ll have more to say about that when Im properly briefed,” he said.

“There are checks and balances in this system and they’ve been deliberately undermined by the former prime minister.”

Former agriculture minister David Littleproud has called on Mr Morrison to explain himself.

“He owes it to the Office of Prime Minister and the exalted position that we have this this country to reflect and actually give an explanation to clear this up and give clarity,” he told the ABC.

“That is the honourable thing to do, to give the respect to the highest office that any Australian can be elected to in this country.”

Independent MP Helen Haines, a key backer of a federal integrity commission, said while there was uncertainty around the COVID pandemic and what would happen if the health minister fell ill, there was no reason for the secrecy.

“But the fact he chose not to tell anyone about this, the fact many members of his cabinet didn’t know about this, but this covered multiple portfolios,” she said.

“The prime minister has a responsibility to inform the parliament, the public and to inform his cabinet.”

On the weekend, The Australian reported Mr Morrison swore himself in as health minister and finance minister, alongside his own ministers, after the start of the pandemic in March 2020.

He also swore himself in as resources minister in 2021 and used his powers to overturn a decision by former minister Keith Pitt to approve a controversial gas project off the NSW coast.

Mr Pitt has said he was unaware Mr Morrison had joint oversight of his portfolio and that he stood his decisions.

A spokesperson for Governor-General David Hurley said he followed processes consistent with the constitution when he appointed Mr Morrison to the additional portfolios.

“It is not uncommon for ministers to be appointed to administer departments other than their portfolio responsibility,” the spokesperson said in a statement.

“These appointments do not require a swearing-in ceremony. The governor-general signs an administrative instrument on the advice of the prime minister.”

Opposition Leader Peter Dutton said he didn’t know Mr Morrison had sworn himself into the cabinet positions.

“Obviously the prime minister had his reasons, his logic for it, but it was not was not a decision that I was a party to or was aware of,” he told ABC Radio on Monday.

At least one legal expert has rubbished the apparent justification for the secret swearing-ins. Patrick Weller, emeritus professor of politics at Griffith University, who wrote the book(s) on cabinet government, said 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,” he said.

“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 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.

Mr Albanese is expected to provide a further update on Tuesday, after a further briefing from the Department of Prime Minister and Cabinet.

-with AAP