In full parliamentary flight this week, Prime Minister Scott Morrison raged at Labor that it had "gone to the bottom of the chum bucket" when it started its probing of links between senior Coalition figures and the travel company HelloWorld.

Chum buckets, for anyone not familiar with the term, are buckets full of fish guts and heads and other smelly stuff that is thrown into the water by fishermen to attract a feeding frenzy of fish, particularly sharks.

And there was some truth to what the Prime Minister had to say, except that the final week of Parliament before the budget is handed down on April 2 and the expected calling of the election saw chum flying in all directions as politicians on all sides desperately flung the blood and gore in the direction of their opponents.

Anxious to see the debate move on from asylum seekers, on which it feels vulnerable, Labor turned to the HelloWorld story, which offered all the best ingredients: special deals and politicians' privileges; the suggestions of politically compromised government contracts.

The Government relentlessly attacked Labor over amendments passed last week giving doctors a greater say in medical evacuations of asylum seekers from Nauru and Manus Island.

Dire warnings continued about paedophiles and rapists and murderers being unleashed on us as a result of the amendments.

Various legal opinions, not actually released, were alluded to.

Pezzullo's intervention an important one

Much of the drama about HelloWorld and asylum-seeker policy flowed out of Senate Estimates Committee hearings.

In the case of asylum-seeker policy, this centred on the evidence of the secretary of the Home Affairs Department Michael Pezzullo, and his officials, on Monday.

The Canberra mandarins who were once seen to wield much power over politics and government have long gone.

Michael Pezzullo is seen as the architect of the huge national security empire he now oversees. ( ABC News: Matt Roberts )

But if there is one figure that does a really good imitation these days it is Mr Pezzullo.

He is seen as the architect of the huge national security empire he now oversees and regularly scares the daylights out of various politicians — and others — when he briefs them on the threats facing the country.

That is what made his interventions on Monday so important.

Apart from making it very clear — as did ASIO head Duncan Lewis — that he didn't appreciate the Government leaking his department's classified advice for political purposes, he also made it known that the Government's central attack on the medical evacuation legislation was wrong; that the amendments would not prompt a flood of new boat arrivals.

While the original amendments passed by the Senate in December would have had a "catastrophic" effect on border protection policy, he said, this was not the case with the modified amendments passed last week.

He did, however, also send a shot across Labor's bows: while the amendments would not of themselves restart the boats, it was imperative that a tough rhetorical line about Australia's resolve be maintained by current or any future government.

We now know a little more

But there was more that emerged from Mr Pezzullo during the hearings, prompted by questions from an outraged Greens senator Nick McKim.

When the Government announced it was reopening Christmas Island, there was confusion over how the facility would actually be used.

Was it being opened in anticipation of new boat arrivals, or as part of a new regime for the existing group on Manus and Nauru?

To some extent, the Government — and the border protection enforcers — clearly like a bit of ambiguity on issues like this: the uncertainty, the argument goes, works in favour of the policy if the people smugglers and refugee advocates aren't entirely sure what the policy is.

But asked direct questions by Senator McKim about the role of Christmas Island, Mr Pezzullo was crystal clear.

Would people being transferred back to Australia from Manus and Nauru, in the wake of the new amendments, be transferred to Christmas Island "in the first instance"?

"That is the policy of the Government. Yes," Mr Pezzullo responded.

Nick McKim said the Government's policy represented an attempt to circumvent the will of the Parliament. ( ABC News: Marco Catalano, file photo )

An angry Senator McKim said this policy represented an attempt to circumvent the will of the Parliament.

The Greens also led an attack on Labor for accepting the policy, given it is quite clear that medical facilities don't exist on the island to treat seriously ill people.

However, Mr Pezzullo also told Senator McKim that "it goes without saying that if a specialist is available only on the mainland, then the mainland will of course be utilised".

So we now know for certain a little bit more about how this new regime will operate.

People assessed on Nauru or Manus — under the new mechanisms supervised by doctors — as needing medical evacuation will be sent first to Christmas Island, where they will then be further assessed for possible evacuation to the mainland.

Legal mechanics largely overlooked

Let's leave aside, for now, the extraordinary costs and time taken in this process of shipping people from a tiny island in the Pacific Ocean to a tiny island in the Indian Ocean and contemplate what lies behind it.

On one level, it is designed as yet another deterrent, another signal to "the people smugglers" that it is not going to be any easier to get to Australia just because you may be seriously ill.

But the legal mechanics of the move have been largely overlooked.

The amendments passed by the Parliament only relate to getting people off Nauru and Manus Island to Australia.

Once people are medically evacuated to Australia, the decisions are once again back in the hands of the minister of the day.

The reopening of Christmas Island gives the control over medical evacuations to the mainland back to Government, rather than doctors.

To the policy's designers, it's a move to stop "sympathetic" doctors assessing people off the island who might not actually be sick.

Combined with the Nauruan Government asserting its right to say who needs to be medically evacuated, the path to people being medically evacuated to Australia does not necessarily seem any clearer than it was before the amendments were passed last week.

And there is another hurdle.

Many refugee advocates believe that the best thing to be done now is to keep to an absolute minimum the people who should be evacuated as the pre-election atmosphere becomes ever more febrile.

Advocates have long argued that asylum seekers are but pawns in a political game.

Indeed, in a High Court action commenced last month, the case is being made that they are in fact being punished and tortured simply as a deterrent to others.

Of all the chum being thrown around this week, it will be asylum-seeker policy which continues to be hurled out, in the hope of attracting the sharks, in the lead-up to polling day.

But for all the blood and guts, the question of how much real change has occurred in our treatment of asylum seekers is very murky.

Laura Tingle is 7.30's chief political correspondent.