Stephen Keim SC said that in light of last week's landmark decision by the High Court, which ruled the Government's so-called Malaysia Solution to be invalid, and the advice of the Commonwealth Solicitor-General released earlier this week, onshore processing should now be the preferred option.

"Onshore processing is the legally certain, least expensive and most humane and principled way ahead for determining asylum-seeker claims," said Keim.

In the High Court decision handed down on 31 August, the Malaysia Solution was deemed unlawful as it did not provide adequate protection to those being sent to Malaysia.

In welcoming the decision, Keim said its significance lay with the fact that it "casts substantial legal uncertainty on a 10-year policy that has been proven to be morally deficient and economically wasteful".

He also said that given the High Court's reasoning, it is unlikely that any of Australia's neighbours - with the exception of New Zealand - would be suitable for processing Australia's asylum seekers.

"The fact remains that Australia, notwithstanding the shortcomings in its own approach to asylum seekers, is in the best position to meet its freely undertaken obligations under international law to ensure adequate human rights protections to people while they are pursuing their legitimate right to seek asylum from persecution," said Keim.

Keim also cautioned the Government against resurrecting the Nauru and Manus Island processing and detention - neither of which has been scrutinised by the High Court. Keim added that even though Nauru has recently acceded to the Refugee Convention, questions remain as to whether its domestic protections would satisfy the criteria under s198A of the Migration Act.

In discussing people smuggling, Keim said the efforts to address it should be centred on strategies that are truly regional in nature.

"These strategies should maximise disincentives for people to seek the services of people smugglers, thereby exposing themselves to the attendant risks. These strategies should at the same time respect and protect the rights and interests of refugees and asylum seekers," he said.

"The resettlement component of the Malaysia Agreement and the commitment of Australia and Malaysia to improve the quality of protection for refugees and asylum seekers in Malaysia are the sorts of steps that would need to be part of a well thought out regional approach."

Keim urged the Government not to be tempted to undermine the High Court's decision through any "quick-fix" legislative tricks, and said any attempts to "by-pass" the decision would likely end up before the courts and further delay the development of a constructive and effective asylum seeker policy.

Keim also said any such moves would reflect poorly on Australia as an international contributor to addressing the global refugee protection deficit.