Former prime minister Malcolm Turnbull says the government led by his successor Scott Morrison is in "plenty of trouble" just months out from the federal election.

This week the federal government has been hit with more poor opinion polling and reports that former New South Wales premier Gladys Berejiklian once described Mr Morrison as a "horrible, horrible person" who cares about politics more than people.

Speaking on the ABC's 7.30 program, Mr Turnbull declared he believes his former federal coalition colleagues are struggling to be re-elected for a fourth term.

"Well, I mean, what is it — it's eight points behind in Newspoll, election is in three months or so. No, it's in plenty of trouble, for sure," Mr Turnbull said.

Mr Turnbull says he wasn't surprised to learn of Ms Berejiklian's apparent description of the man who took over from him as Prime Minister.

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"I wasn't surprised by the content. I was a little bit surprised they found their way into the public domain," he said.

"Clearly, whoever authorised [Network 10 journalist] Mr [Peter] Van Onselen to release that did not have Scott Morrison's best interests at heart," he said.

Asked which federal minister he believed was responsible for releasing the private text messages, Mr Turnbull joked, "Colonel Mustard in the library with a smartphone".

Appearing on 7.30 after Mr Turnbull, Defence Minister Peter Dutton has emphatically defended Scott Morrison, saying "he puts the interests of this country first and foremost".

"Most Australians see they've got a Prime Minister who is human like the rest of us, doesn't get everything right, but dedicates himself each day to get us through the realities of COVID," Mr Dutton said.

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Turnbull says newly released email shows French were lied to over submarines

Mr Turnbull had appeared on the 7.30 program to discuss documents revealing Australia's defence leadership received positive advice about the French submarine project, just weeks before it was scrapped in favour of the AUKUS nuclear deal.

An email, obtained under Freedom of Information laws, reveals a message from Defence secretary Greg Moriarty to the department's submarine boss Greg Sammut, indicating positive feedback about the submarine deal would be passed on to France in August.

"I will ensure that the good progress to date is part of the advice we take to government, and you will hear that message repeated in the 2+2 with France and in other engagements," the email said.

Mr Turnbull, who was prime minister when the submarine deal was clinched in 2016, said the emails confirmed the French had been lied to.

"The Australian government did not give the French any reason to believe that the project was about to be cancelled," he told the ABC.

"This was a diplomatic debacle of the first order, and the consequences have been it's undermined Australia's honour, security and sovereignty."

Mr Dutton denies the French were misled, saying the emails needed to be viewed in context.

"There was no lying to the French, we were very clear in our position," he said.

"The Prime Minister made it clear to [French] President [Emmanuel] Macron in the dinner they had in Paris that the circumstances had changed in the Indo-Pacific and not for the better."

"The only option for us was to go with a nuclear submarine and that's exactly what we did and it's a decision I very much stand by."