Enter Lindsay Tanner.

Any discussion about his current rant about the Labor Party must first give him credit for making the threshold decision to leave the team as a matter of principle.

Labor needs thinkers like Tanner and his departure was a big loss to the government.

That loss was compounded when his retirement heralded a win by the Greens' Adam Bandt in the inner Melbourne seat.

Tanner announced his retirement in Parliament during Julia Gillard's first question time as Prime Minister.

The message about the coup was clear. He stood by his principles which dictated he couldn't work with the new PM.

This year, when Rudd challenged to regain the leadership, the bid was supported by another cabinet member, Chris Bowen.

After that failure, Bowen did not believe he had to resign from cabinet led by the person he did not think was the best one to be PM. His punishment was to continue in the immigration portfolio and be forced to maintain cabinet solidarity.

We await his book when he retires some years hence.

Mark Latham shone brightly in the art of biting the hand that fed him so well for so many years.

His caustic observations of colleagues was published as The Latham Diaries.

In late 2010, he observed that ''the lasting impression from the Rudd years is one of emptiness'' and described Rudd's prime ministership as an exercise in populism. His conclusion was that Labor had lost its way.

''I'm a hater,'' Latham is quoted as saying in 2002. A decade later the emotion was reciprocated by his former colleagues.

Now comes Tanner's book - arriving just as Labor is showing signs of a mild recovery in the polls.

Gillard is clearing the decks of troublesome issues, preparing to begin a major campaign from February to win back the hearts and minds of disillusioned Labor supporters before the election.

Despite that, the party has the capacity to rip itself apart.

Tanner insists he is not trying to kick-start a renewed campaign to return Rudd to the leadership.

And that argument is believable - Tanner is too far removed now to have influence within caucus.

But the core thrust of his criticism is a searing indictment of Labor's style and, by implication, Gillard's leadership style.

He denies the latter.

Party members-cum-critics before him have wailed over Labor's capitulation to pragmatism over principle. Their prime exhibit is the government's enthusiastic embrace of much of John Howard's Pacific Solution to deal with asylum seekers.

Tanner's arguments are credible because he was at the heart of cabinet decision-making.

And that was a mess, according to his book, which points to a collapse of process.

But in interviews to promote the book, he says extreme and grossly exaggerated statements were made by cabinet colleagues about Rudd's management style. They were possibly the most vicious series of public attacks on a minister ever.

Well, which is correct? Does he believe cabinet was dysfunctional under Rudd, or not?

In Parliament, rising to announce his retirement, Tanner said: ''This decision is totally, absolutely unconnected with the events of the past 24 hours.''

The general consensus at the time was - absolutely, totally unbelievable.

In a later interview, he resolved not to be a commentator. ''I'm not a kiss-and-tell kinda guy.''

But Gillard is the kiss-and-tell type. When Rudd tried to challenge earlier this year, the PM told the public what she had not done at the time of the coup - explain why Rudd was dumped.

''Kevin Rudd as prime minister always had very difficult and very chaotic work patterns,'' she said.

Her senior ministers unleashed an extraordinary cacophony of criticism about him. One MP described him as a psychopath with a giant ego.

Since then, something has changed as Tanner ruminated over his book.

Now he is the kiss-and-tell type, but insists whatever his criticisms of Labor might be, it does not reflect on Gillard's leadership.

How can that be?

In a feisty exchange with Leigh Sales on ABC TV, Tanner defended this position.

He had questioned the war in Afghanistan, the level of the dole and the proposed media regulator.

Question: Given that right there you've criticised three major areas of government policy, given your criticisms about the Labor Party's direction more broadly, the logical conclusion for one to make is that you think Julia Gillard is a poor Labor leader.

Tanner: No, I don't think there's any logic in that at all. In fact that is a …

Q: Well, how can there not be logic in that?

Tanner: No, well, that is a classic non sequitur. It is possible to have a point of view that is different from somebody else's on a particular issue without thinking that they are a good leader, a bad leader or anything else.

Q: Really?

Tanner: Yes.

Q: So you think the direction of the Labor Party is disastrous. You think some of their policies are not effective. Yet you think that Julia Gillard's a great leader.

Tanner's book suggests Labor is ''an electoral machine largely devoid of wider purpose'' and says the party needs a ''complete root-and-branch rethink about why we exist''.

Backpeddling, he says his criticism is not about the Labor Party or the government, per se.

''It is about a phenomenon that has been in place for the best part of 15 years or so, so it has been a gradually evolving problem,'' he says. That just doesn't ring true.

Here we have one of the key players in the Rudd cabinet's ''gang of four'' laying a generous dollop of criticism on the government led by Gillard, but insisting he is not doubting her performance as leader.

Tanner's intervention is good news for Tony Abbott. It's a distraction from his current problems.

Overseas, Gillard treated Tanner's comments with disdain. From her perspective, the blast from the past has been long expected, ever since Tanner's dramatic resignation announcement took the edge off her first day in the top job.

In Washington with her, Bob Carr dismissed the seriousness of the observations. ''We went through a stage where every galah in a pet shop had an opinion about what was wrong with the Labor Party.''

Labor strategists hope to regain his former seat in Melbourne at the next election but at this stage they don't know which side of the chamber the (they hope) new Labor MP will be sitting on.

Ross Peake is Political Editor

Twitter: @rosspeakeCT