The High Court of Australia has been asked to consider whether the separation of powers doctrine should, and if it currently does, apply to the Northern Territory as part of a challenge to the territory's paperless arrest laws.

The laws brought into force in the NT in December last year allow police to arrest people and hold them for four hours, and longer if intoxicated.

People can be held on suspicion of minor offences until officers decide whether to release them without charge, issue a fine, release them on bail or bring them before a court.

Kumanjayi Langdon died three hours after being taken into police custody. ( Supplied with permission of cultural brother Rex Granites )

In August, the inquest into the death of an Aboriginal man held under the paperless arrest laws at the Darwin CBD watch house was told similar deaths would occur if the regime was not repealed.

Kumanjayi Langdon, 59, from Yuendumu in Central Australia, died in May three hours after being taken into police custody under the paperless arrest scheme for "drinking in a regulated place".

In his findings, coroner Greg Cavenagh said the laws were "manifestly unfair" because they disproportionately targeted Indigenous people, and were "irreconcilable" with the 1991 royal commission findings that arrest should be used as a last resort to prevent deaths in custody.

"It is no coincidence that the first man to die under the laws is an Aboriginal man," Mr Cavanagh said.

He said the law "in my view perpetuates and entrenches Indigenous disadvantage".

The coroner recommended the repeal of the law "to prevent the risk of an increase in deaths like Kumanjayi Langdon's".

NT Attorney-General John Elferink stood by the laws and said high Indigenous incarceration rates had more to do with "lifestyles" and "passive welfare".

The North Australian Aboriginal Justice Agency (NAAJA) is challenging the laws on the basis that the NT Government legislated to give the territory's police punitive powers that only the courts should have, according to the separation of powers doctrine.

This doctrine ensures that the parliament, executive and judiciary arms of government have different roles to play in making and managing laws.

"One consequence of the separation of powers is that the parliament cannot invest judicial power otherwise than in accordance with the constitution," the NAAJA's senior counsel Mark Moshinsky argued in the agency's court submission.

"The NT executive cannot exercise judicial power ... only NT courts can do so.

"The second reading speech for the bill makes plain that these new powers were intended to provide police with an easier way to 'clean up the streets' and that the bypassing of the courts was deliberate.

"The Attorney-General described them [saying], 'It will give police a vehicle by which to remove them, contain them and then release them'.

"This is one of those rare cases where ... [the laws] authorise detention because the legislature wishes to punish or penalise those liable to detention without the safeguards of a judicial hearing."

NAAJA argued the laws postpone for four hours any decision on whether to bring someone before a court or offer them bail.

Separation of powers doctrine 'has no application in territories'

Yet according to Solicitor General Michael Grant who is representing the NT Government, the territory is not and should not be bound by the separation of powers doctrine.

"The Northern Territory has established a number of courts and tribunals which exercise both judicial, and non-judicial functions," he said.

"It has done so on the basis of a view that the doctrine of separation of powers has no application in territories."

Mr Grant said that to conclude that the doctrine of separation of powers operates in the NT would "invalidate the decisions of these courts of tribunals".

"The maximise flexibility, the parliament must be free to make whatever arrangements it wishes in respect of a territory judiciary, including both legislating for and maintaining control and administration of the judiciary and completely transferring control and administration of the judiciary to a separate territory politic under its own legislation.

"Imposition of the doctrine of separation of powers particularly at this stage of [the Northern Territory's] constitutional development would be obsolescent and debilitating."

The Government also argued the powers it gave to the police were not punitive.

"Arrest and detention in custody ... of a person accused of crime to ensure that they are available to be dealt with by the courts is not punitive and does not appertain exclusively to judicial power," Mr Grant said.

The hearing is set to continue tomorrow.