The test case was brought by a Bangladeshi plaintiff, who claimed that the government’s detention of her as an asylum seeker on Nauru was unlawful.

UNSW Professor George Williams told Lawyers Weekly that the High Court decision makes it difficult for lawyers to challenge the legal basis of offshore detention in the future.

The High Court made a similar ruling in 2014 with respect to Manus Island, he said.

"The result of the case is that the government has been given truly extraordinary powers over some of the most vulnerable people imaginable and that those powers can be exercised in a way that can lead to great harm being caused to those people, particularly children," he said.

Prior to the decision, Immigration Minister Peter Dutton said the government intended to send 160 adults, 37 babies and 54 children currently in Australia back to Nauru if the High Court ruled that such a move was legal. 

Australian Lawyers Alliance spokesperson and barrister Greg Barns said the offshore detention of children, in particular, leaves Mr Dutton open to claims that he breached duty of care.

“It is also arguable that such conduct would amount to a breach of the Commonwealth Work Health and Safety Act,” he said.

The act makes it an offence to allow persons to be present in unsafe workplaces, irrespective of whether those persons are visitors, residents or workers, according to Mr Barns.

Professor Williams agreed that the government could be exposed to these kinds of legal attacks, but said any further action would only be “picking away at the edges”.

“[It] won’t fundamentally overturn the regime,” he said. “It may cause some inconvenience, but really it’s at the margins because the big cases have been lost.”

He also disagreed with UNSW research associate Madeline Gleeson, who argued in a recent opinion piece that the High Court ruling leaves “small but significant glimmers of hope for asylum seekers”.

“I guess the question is whether 'glimmer' is overstating things,” he said. “That's the sort of level we're at.”

Ms Gleeson said the High Court decision has “dealt a blow” to the government’s argument that it has no responsibility for what happens in offshore detention. The High Court also “left the legal door slightly ajar” by agreeing that offshore detention should not go beyond what is reasonably necessary for processing, she said.

Professor Williams agreed that the High Court has laid down some parameters in the decision but said that it is not difficult for the government to stay within those parameters.

“Essentially the High Court has upheld a regime that enables people to be removed immediately, without processing, to a country where there is no requirement that their basic rights are respected. That can apply to children of any age. It is not clear what more [the government] would want anyway.”

Professor Williams said the High Court ruling was made possible by the lack of strong human rights protections in Australia.

“In our legal system that outcome isn't only possible, it's even probable in many cases […] because we don't even get to first base in many respects of protecting the human rights," he said.

“Australia is now the only democratic nation in the world that doesn't set out a comprehensive regime of human rights protection in the form of a Bill of Rights.

“This decision really does emphasise what it means to live in a country where there isn't adequate human rights protection.”

The other contributing factor in this High Court decision is that the two major political parties are in “lock-step” when it comes to offshore detention, he said.

In June 2015 the government enacted Section 198AHA of the Migration Act to “buttress and authorise these types of regimes”.

“That special law was passed just in the space of two days through Parliament and what that did was actually retrospectively validate a lot of the conduct that we are talking about,” Professor Williams said.

Two days before the High Court was to hear the case, the Nauru government announced that the detention centre would be opened, further destabilising the plaintiff’s case, according to Ms Gleeson.