Labor’s national president Mark Butler has denied an election campaign review blames Bill Shorten for the party’s failure to win government, as speculation swirls about the contents of the “secret” document.

Amid suggestions the party’s post-mortem was critical of Mr Shorten, Mr Butler said on Sunday the review had not found the Opposition Leader’s popularity had been costly to Labor.

“As the person who chaired that review, and I was a very big part of us encouraging us to conduct the review that we conducted, I can say categorically that it was not there,” he told the ABC.

“The conclusion of the review is the one that most objective observers would make, and that is that we conducted a very good campaign led by Bill Shorten.”

The Seven Network reported last week that Labor’s campaign review found the party would have won government if it were not for Mr Shorten’s poor personal approval ratings.

The decision not to release the review, even within the party, has angered senior figures, Seven reported.

Bill Shorten remains less popular than Malcolm Turnbull. Photo: AAP

But Mr Butler said the decision was “not unusual”.

He said the report was a “nuts and bolts review of the machinery of the campaign” and claimed such documents were often kept from the public.

“From time to time, we release different reviews which are intended to engender a more broad-ranging debate within the party and within the community about our culture and rules and such like,” he said.

“That type of review is publicised, but obviously, an internal mechanical review about the machinery of our campaigning is never circulated or published widely, and this year’s review wasn’t either. That’s not unusual.”

Labor close but no cigar in 2016

Labor won 69 seats at the 2016 election, up from 55 in 2013, while the Coalition claimed 76, which was just enough to hold onto power.

While Labor has polled ahead of the government in two-party preferred terms across 20 consecutive Newspolls, Mr Shorten continues to lag behind Mr Turnbull as preferred prime minister.

The latest Newspoll, published on Sunday night, had the ALP ahead of the Coalition 54 to 46 per cent on two-party terms, and 37 to 36 per cent on primary support.

In the same poll, the Labor leader improved his ‘preferred PM’ rating by two percentage points to 33 per cent, while the Prime Minister dropped one point to 41 per cent.

As The New Daily has reported, both leaders have recently increased their appearance on FM radio, presumably in a bid to shore up their personal approval ratings.

Mr Shorten has brushed off criticism of the election report’s secrecy, saying “reviews sometimes get released, sometimes they don’t”.

“One thing is for sure though, the Australian people looked at Labor within one term of our defeat in 2013 and took a much greater interest,” he said last week.

Opposition frontbencher Anthony Albanese, who lost Labor’s 2013 leadership contest to Mr Shorten, also came to his leader’s defence.

Asked if Labor would have won if he was leader, Mr Albanese said: “Look, we did very well in the last election.

“We won seats right around the country … And you know what characterises Labor? We’re a team.”

Mr Albanese sparked headlines earlier in the year by pointedly criticising the ‘Australians First’ ad starring Mr Shorten, which was subsequently branded racist.

The Liberal Party’s election review, which was released in April, said the party had failed to rebut Labor’s so-called ‘Mediscare’ campaign.

Labor’s 2013 election review was released publicly and remains available on the party’s website.