Former prime minister Tony Abbott has refused to defend Scott Morrison’s decision to secretly appoint himself to five ministries, following scathing advice from the nation’s top lawyer.

Mr Abbott’s blast came as Coalition frontbencher Stuart Robert accused members of the government of a “witch hunt” over the secret portfolio grab.

It followed scathing legal advice from the solicitor-general that Mr Morrison was validly appointed to the role of resources minister in April 2021, not the other four portfolios he also took on.

The solicitor-general found Mr Morrison’s appointment was valid but “inconsistent with the conventions and practices that form an essential part of the system of responsible government”.

“I’m just not gonna (sic) defend what was done,” Mr Abbott told Sky News on Tuesday.

“On the other hand, we’ve got a report from the solicitor-general. It clearly says that there was nothing illegal done, but it also clearly indicates that it is just highly unconventional, highly unorthodox and shouldn’t have happened.”

After the legal advice was released on Tuesday, Prime Minister Anthony Albanese announced an inquiry would be held.

Attorney-General Mark Dreyfus said the legal advice was “deeply alarming”, reinforcing the need for an inquiry.

“We’re going to have an inquiry, we’re just now working out the details of that inquiry so that we can look into exactly what happened, and then get some recommendations to make sure that it never happens again,” he told the Nine Network on Wednesday.

“It’s not the end of the matter.”

Deputy Prime Minister Richard Marles has warned that Mr Morrison should face “severe consequences” for the controversy – prompting Mr Robert to allege his comments pointed to ulterior motives.

“Mr Marles’ comments sounds like a political witch hunt,” he told ABC Radio on Wednesday.

“When you hear the Deputy Prime Minister, Richard Marles, speak yesterday morning that Mr Morrison must pay a high political price for this, you start to wonder what the government’s intent is.”

Mr Robert said the solicitor-general’s advice was sensible and that it pointed out a road map for reform.

The Greens are seeking a privileges committee inquiry into whether the former prime minister misled parliament.

However, House of Representatives Speaker Milton Dick has rejected the push, according to The Guardian.

MPs could still vote to refer Mr Morrison to the committee but would require a majority.

When asked if an inquiry was necessary, Mr Abbott said: “When you don’t get good, sensible behaviour, the best recourse is through the political process.”

“I suppose that’s what we’ve seen happening in Australia,” he said.

Former Liberal foreign minister Julie Bishop said she understood why the government had announced an inquiry into Mr Morrison’s secret ministries.

“The solicitor-general’s advice does raise a number of questions that I believe should be examined,” she told the Nine Network on Wednesday.

“It will have to be a non-political inquiry. It can’t be headed up by, for example, the head of prime minister and cabinet because presumably what the departmental offices knew would also be the subject of the inquiry.”

Mr Morrison has indicated he would take part in the inquiry should it be a “process to learn lessons from the pandemic”.

Mr Dreyfus said the comments weren’t surprising.

“Of course [Mr Morrison] wants it to be broader, and of course, he wants to hide behind the pandemic,” he said.

“This has nothing to do with the pandemic, this was just a power grab by Morrison.”

Liberal deputy leader Sussan Ley said the Coalition acknowledged the process of appointments could be made more transparent and pledged to work with the government.

“The opposition is ready to proceed along those lines with the government with the proposals to improve those processes,” she said.

“There are issues to be dealt with that the solicitor-general has made us aware of in his report … and that will happen.”

Mr Morrison said it was essential to reflect on some of the decisions and “lessons learned”.

“The solicitor-general has noted a number of these points from his perspective in his advice and I am sure this will help guide any changes in these areas,” he said.

-with AAP