The federal government's top legal adviser has confirmed it may be impossible to resurrect the Howard government's asylum seeker detention centres in Papua New Guinea and Nauru under current laws.

Stephen Gageler has given the government written advice confirming the High Court's decision to scuttle the controversial Malaysian people swap deal last week has far-reaching implications for all offshore processing.

Mr Gageler and two other senior counsels, Stephen Lloyd and Geoffrey Kennett, say they "do not have reasonable confidence" that the government could legally send asylum seekers to Papua New Guinea and Nauru as a result of the judgment.

The lawyers say Nauru's decision to ratify the UN Refugee Convention this year "raises the possibility" that a government could use its power to send asylum seekers to Nauru in the future but only if it could satisfy a court there were appropriate protections in place.

"These are complex issues of fact and degree requiring detailed assessment and analysis," the advice reads.