The Federal Opposition says it is willing to talk to the Government about changing Australian law to allow the offshore processing of asylum seekers.

The Government is not ruling out amending the Migration Act, after revealing it received legal advice that offshore processing would be difficult, if not impossible, to implement under current law.

Solicitor-General Stephen Gageler's advice was commissioned after the High Court ruled the Government's Malaysia refugee swap deal to be invalid.

Mr Gageler warns current law would not allow the re-opening of the detention centres on Papua New Guinea or the Pacific island nation of Nauru.

The Government will need the Opposition's help if it wishes to pass changes to the Migration Act, after the Greens said they would not support any changes.

Opposition Leader Tony Abbott says if the Government wants to amend the Migration Act he is ready to cooperate.

"We don't want the Government to use the High Court's decision and the solicitor-general's opinion to drop offshore processing, because offshore processing is an essential part of any effective plan to stop the boats," he said.

Immigration Minister Chris Bowen says the Government will use the solicitor-general's advice to determine its next policy step.

"What the solicitor-general's advice today says is that it would be difficult under existing laws, under existing legislation, to pursue offshore processing in New Guinea or Nauru, or for that matter in many countries," he told ABC's Insiders program.

Opposition immigration spokesman Scott Morrison says the Coalition is willing to talk about changes to law, but Labor must decide what it wants.

"If the Government is interested in proceeding with re-opening Nauru then all it has to do is talk to the Coalition; they need to put up their case," he said.

"[The Government] need to demonstrate what changes are necessary if indeed any changes are necessary, but that is a case for the Government to make and the Opposition is happy to talk to the Government."

Still an option

After Thursday's High Court ruling, Mr Abbott said the Government was wrong to believe the judgment meant asylum seekers could not be sent to Nauru.

The Coalition's legal affairs spokesman, George Brandis, says Nauru is still an option even without a change to the Migration Act.

"The Government is trying to misrepresent the effect of the solicitor-general's opinion by claiming falsely that it makes it impossible to prosecute the Nauru solution. Any minister who says that is just lying," he said.

But Mr Bowen says that is not the case.

Sorry, this video has expired Bowen discusses offshore processing advice

"Quite clearly under all the legal advice, if Mr Abbott wanted to go down the Nauru option he would need legislative change," he said.

"What is very clear from the High Court judgment is you could not send unaccompanied minors in any workable way to Nauru or anywhere else."

More than 330 asylum seekers the Government wanted to transfer to Malaysia are in limbo on Christmas Island until a decision is made on where to send them for processing.

Labor's left faction wants an end to offshore processing, a position Greens' Senator Sarah Hanson-Young agrees with.

"The majority of Australians support assessing the needs of asylum seekers here in Australia," she said.

"It's the cheapest option, it's the most humane one, it's simple.

"The Government simply needs to do away with this idea of offshore processing and get back to basics."

'Silly' attack

Meanwhile, former prime minister John Howard has joined those condemning Prime Minister Julia Gillard's criticism of the High Court over the asylum seeker decision.

During the week Ms Gillard called the High Court's ruling "deeply disappointing" and said it contradicted precedents set by other courts in challenges to the Migration Act.

A number of frontbenchers threw their support behind Ms Gillard as she defended her right to criticise the judgment.

But Mr Howard says Ms Gillard should have simply accepted the court's decision.

"We've now got a situation where the Prime Minister is questioning the intellectual consistency of the Chief Justice of the High Court, well that's a very silly thing to do," he said.

Mr Bowen defended the Prime Minister, saying she was justified in making her comments.

"That's not a criticism it's just a statement of fact," he said.

"If you compare what the Prime Minister said to what ministers in the previous government said when they lost High Court cases, there's no comparison at all."