Royal Commissions are not for political retribution and using them as such is inherently dangerous. In light of the Ashby affair, the Abbott Government should be treading more carefully, writes Darrin Barnett.

Let's be clear about this: former prime minister Julia Gillard's appearance at the Trade Union Royal Commission today is a witch hunt. Just like the most recent investigation into the failed pink batts scheme, it reeks of payback.

The point of the process is to reinstate the smear that dogged her prime ministership. It is yet another chapter in the LNP's long-running attempts to destroy her.

Gillard has been grilled for 20 years now on the dealings surrounding her relationship with former Australian Workers' Union official Bruce Wilson.

Suggestions of alleged impropriety over a so-called slush fund and purchase of a suburban property in Melbourne have been forensically examined.

Gillard has consistently said she did not act improperly and did nothing wrong. Despite today's appearance at the Royal Commission - plus myriad press conferences, questions in Parliament, and well-resourced investigative reporting - there is still no smoking gun.

From mid-2012 onward, in my role as press secretary to Ms Gillard, our team was bombarded with reiterations of the same questions over and over.

We generally referred to answers given previously, including those at the PM's marathon press conference in August 2012. There was nothing new to report.

Gillard aptly described the haters as "misogynists and nut jobs on the internet", and you can expect this group to be desperately cashing in on their last chance for airtime and column inches on the topic in the coming days.

Yet what is significant is that the goalposts have now been shifted significantly on what is to be investigated at the behest of the government of the day.

To give an indication of the LNP's motives for chasing Gillard, LNP frontbencher Julie Bishop told the Sunday Telegraph in February 2013 that she only agreed to pursue Gillard after the Prime Minister accused Abbott of misogyny.

"Tony had always given Gillard the benefit of the doubt, he'd always thought there was a line she would never cross," the now Foreign Minister said.

"She crossed the line that day, and as far as he was concerned, all bets were off. So it ultimately backfired on her, because I would never have raised the AWU matter had she not done that."

Meanwhile, the Royal Commission into the previous government's flawed Home Insulation Program handed down its report last week with Commissioner Ian Hangar, QC, finding the Labor government should have done more to ensure the safety of the four young men who died, as well as other inexperienced workers.

However, Opposition attorney-general Mark Dreyfus is right to point out that the $20 million spent on the Royal Commission has not significantly altered the account of the insulation scheme that the previous eight inquiries had provided.

There had already been coronial inquiries in New South Wales and Queensland into the deaths. The cause of death is known. Three of the four employers have been prosecuted and convicted.

There is a fair argument that no modern workplace deaths have been more thoroughly examined, even before the Royal Commission. So why hold one?

In addition to all this, we have further questionable overstepping of conventions with Mr Abbott personally approving a decision to make cabinet documents available to the HIP Royal Commission.

Former prime ministers Bob Hawke and Malcolm Fraser both expressed concern at the decision to hand over cabinet documents - citing a fear it would endanger the convention of cabinet confidentiality.

"Ministers should not have to look over their shoulders and wonder, how will this look when the next government publishes what I am now saying?" Mr Fraser pointed out.

Quite simply, Royal Commissions are not for political retribution and using them as such is inherently dangerous. If for no other reason than narrow self-interest, the Abbott Government should be treading more carefully.

With James Ashby telling 60 Minutes that Christopher Pyne knew of his sexual harassment allegations against Peter Slipper and about the staffer's proposed litigation against the speaker, it is reasonable to conclude that the process was as much political as personal.

"I don't think it's in the interests of the country or the public for there to be a constant trawling over of a two-and-a-half year old story," Pyne said. Mr Abbott says the matter is now closed.

But why wouldn't Labor or another party go to the election seeking a Royal Commission into the Ashby affair?

Why not define terms of reference so that Abbott, Pyne, Mal Brough, and Wyatt Roy, are all put on the stand?

What other text messages are out there? Were there emails? Are there others who would have something to say under oath?

And what about Operation Sovereign borders? At least two people have died, and the entire exercise is shrouded in secrecy. Surely a Royal Commission there would be imminently defendable given recent precedent.

But for any Opposition with the trigger finger itching, there is also an instructive inquiry underway which shows that things can get out of control.

NSW's Independent Commission Against Corruption (ICAC) investigation, set up by an incoming LNP government, has forced no fewer than nine Government MPs to move to the cross benches, while ending the ministerial careers of NSW Premier Barry O'Farrell and Federal Assistant Treasurer Arthur Sinodinos.

When you call for an inquiry you have to be careful what you wish for.

Darrin Barnett is a former Canberra Press Gallery journalist and press secretary to prime minister Julia Gillard. He is now a fellow of the McKell Institute. View his full profile here.