A leading expert says Scott Morrison’s “misleading and deceptive” bushfire ad raises “serious integrity issues” and must prompt reforms to Australia’s weak government and political advertising rules.

Morrison has faced a barrage of criticism since releasing a promotional video spruiking his government’s response to the bushfires at the height of the crisis on Saturday.

The video was party political, authorised only by the Liberal party and Scott Morrison personally, rather than the Australian government.

The Griffith University integrity expert Professor AJ Brown, also a board member of Transparency International, said this made the ad both misleading and divisive, making it an “own goal” for a prime minister trying belatedly to restore public trust.

“I interpreted it, and I think thousands of people interpreted it, as a piece of government advertising, attempting to communicate the Australian government response,” he said. “And that is later how the prime minister tried to explain it.

“But clearly it was not that. It was a party political advertisement, and deceptive, as it became a claim that the Liberal party, not the government and Australia’s own taxpayers were the ones putting ‘boots on the grounds’, sending navy ships and supplying masks.”

“That is atrocious not only because it was factually wrong, but because of its divisiveness.”

Brown, who is currently completing Transparency International’s national integrity system assessment of Australia, said all political parties must give support to fixing the culture and rules allowing political self-promotion.

“Every new prime minister promises the nation they will govern for the whole nation, not just those who vote for them. But in a time of crisis, this rushed attempt to play ‘catch up’ with public trust has created the reverse impression across much of the nation.”

Morrison has defended the ad, saying he chose to publish the ad from his own office because following normal government advertising processes would have meant ‘problems of its own’.

Advertising campaigns by the Australian government generally must comply with a framework of rules and guidelines, which, among other things, prevent the use of public funds for party political advertising.

Before the government advertising framework was introduced in 2008, the Senate Finance and Public Administration References Committee recommended rules were needed to prevent the line between political and government advertising from being blurred.

“The problem with government advertising arises when the distinction between legitimate government advertising for public policy purposes and political advertising for partisan advantage is blurred,” the committee said. “In other words, the problem arises when governments use taxpayer funds to gain political advantage through partisan promotion of their views or themselves, rather than to meet the genuine information needs of citizens.”

Morrison has denied the video was an advertisement, and rejected suggestions it was politically motivated.

“It wasn’t a Liberal party-sponsored ad, it was authorised by me – I’m the leader of the Liberal party – that’s the only authorisation I can post on something that is posted on my page,” he said.

“The same thing that applies to other politicians in Australia … it is simply complying with requirements of Australian law.”

But the University of Queensland politics and law expert Professor Graeme Orr said such material only required political party authorisations if they were deemed “electoral matter”.

Orr said that excluded communications “whose dominant purpose is to educate … on a public policy issue, or to raise awareness of, or encourage debate on, a public policy issue”.

But ... it only requires party authorisation if it's "electoral matter". From which his 2018 amends exclude 'Communications whose dominant purpose is to educate ... on a public policy issue, or to raise awareness of, or encourage debate on, a public policy issue' https://t.co/8BXsRNJDIo — Graeme Orr (@Graeme_Orr) January 5, 2020

Orr said the ad could voluntarily have been authorised to the Australian government, rather than the Liberal party.

“Either [the ad was] rushed without legal advice, his MP allowance used, or someone wanted it to look like Lib Party paid,” Orr tweeted.

We’re putting more Defence Force boots on the ground, more planes in the sky, more ships to sea, and more trucks to roll in to support the bushfire fighting effort and recovery as part of our co-ordinated response to these terrible #bushfires pic.twitter.com/UiOeYB2jnv — Scott Morrison (@ScottMorrisonMP) January 4, 2020

Brown said if the ad was truly designed to provide public information, Morrison could simply have authorised it as “Scott Morrison, Prime Minister of Australia” – not as a Liberal party product – and asked for it to be distributed it through government channels, not Liberal party ones.

“If designed to skirt around the government advertising rules, then these rushed decisions raise serious integrity issues, because Australia’s rules for controlling deceptive political advertising are even more non-existent,” he said.

“Many will simply judge [the bushfire ad] as offensive and politically immoral, but overall it confirms that when under pressure – just when leaders are struggling to restore some kind of trust – our integrity rules and processes are falling down because the confusion made it worse,” he said.

“Added to the obvious ignorance or misjudgment of those who actually made and published the ad, the consequence was inaccuracy, politicisation and partisanship just at the moment where even the prime minister was probably trying desperately to rise above those goals.

“This is a tragedy not just for bushfire victims, but for public trust in all the institutions we are hopefully now triggering to deal better with such disasters. We have to make sure integrity reforms in 2020 mean it can never happen again.”

The ad has also faced criticism from the Australia Defence Association, which objected to the use of the Australian Defence Force for politically motivated advertising.

The ADA executive director, Neil James, said the ad was “plain wrong” and broke longstanding conventions on the use of the ADF in advertising.

“It’s simple: you don’t use the defence force for party political advantage,” he told Guardian Australia.

“They put out a media release giving people all the information so you have to ask yourself what the purpose of the ad is, and the purpose is clearly party political advantage. And that is just plain wrong.”