Simon Birmingham unclear on whether he shared finance portfolio with Scott Morrison

Senator Birmingham became minister for finance in October 2020. (ABC News: Matt Roberts)

Former government frontbencher Simon Birmingham says he remains less than "100 per cent" clear on the extent of the overlap between himself and the former prime minister Scott Morrison in the role of finance minister. 

Yesterday it was revealed that Mr Morrison had appointed himself as the joint minister for health, finance and resources, but not all ministers — nor the Australian public — were told he had done so.

Senator Birmingham became minister for finance in October 2020 and held the position until his party's electoral defeat in May.

This morning, he told ABC Radio Adelaide that he recalled there being "discussion" around Mr Morrison becoming joint health minister, but nothing about him in the finance portfolio.

"In terms of Scott Morrison being sworn in to the health portfolio, I can recall a discussion at some point at the very early days of the pandemic when extraordinary powers were being used, that he had had himself sworn in to that as well just as a precaution," Senator Birmingham said.

"I don't recall something specific to finance at the time, but there were similar decisions being made around finance."

Asked to clarify whether their time in that role had overlapped, Senator Birmingham responded: "I'm not 100 per cent on that, to be clear."

"It has been reported now that he [Mr Morrison] was sworn to that portfolio before I became the finance minister," he said.

"The public reports all relate to a period that goes back to when Mathias Cormann was the finance minister, not me.

"If it were the case, I would certainly prefer to have known, but as I say, I'm not aware as to whether it was the case still by the time I took the portfolio on."

Simon Birmingham speaks to ABC Radio Adelaide's Stacey Lee, Nikolai Beilharz and David Bevan.

Mr Morrison today apologised to Mr Cormann for keeping the move secret from him, saying he assumed the decision had been passed on by his office.

Senator Birmingham was adamant that, during his tenure, the relevant ministerial powers had been his and his alone.

"Scott Morrison can explain his decisions, I can only speak for what I know, and that is in my time as finance minister, the powers as finance minister were solely exercised by me," he said.

"If he was still sworn at some subsequent point whilst I was the finance minister, I'm confident that no powers were exercised and that all decisions were made appropriately by me as the finance minister."

Senator Birmingham said he was not aware of any other portfolios taken on by the former prime minister.

Hours later, current Prime Minister Anthony Albanese revealed Mr Morrison was also appointed to Treasury, Home Affairs and the broader Industry and Science portfolio between March 2020 and May 2021.