The Commonwealth has formally conceded evidence used to demonstrate an Indonesian was an adult rather than a child during a people smuggling case was unreliable, as a court considers whether to quash the conviction entirely.

Ali Jasmin was convicted and jailed in 2010 for five years in a maximum security Western Australian prison, despite documents showing he was 13 at the time of his arrest.

From a fishing village on the island of Flores, he was recruited as a cook on a people smuggling boat stopped by Australian authorities while carrying 55 Afghans near Ashmore Reef in December 2009.

He is seeking to have his conviction overturned in an appeal considered a test case for 14 other Indonesians released in 2012, along with Mr Jasmin, by then attorney-general Nicola Roxon due to doubts about their age.

The Commonwealth policy at the time was that any members of a people smuggling boat crew found to be a child should be returned home rather than face charges.

During a hearing in the Western Australian Criminal Court of Appeal today, Commonwealth prosecutor Kate Gregory said evidence which had found Mr Jasmin was over 18 at the time of his trial was legally "unsafe", meaning it was based on unreliable evidence.

After his arrest in 2009, the Department of Immigration found Mr Jasmin was a child, but this was later overruled by the Australia Federal Police who used a now discredited wrist X-ray to determine Mr Jasmin was an adult.

He was convicted despite an Indonesian birth certificate and family registration document putting his age as 13 at the time of his arrest.

These documents were never tendered as part of Mr Jasmin's defence.

The court of appeal has asked Mr Jasmin's lawyers and the Commonwealth for submissions on whether it has the power to set aside Mr Jasmin's 2010 conviction and acquit him, despite the fact he pleaded guilty to the charge at the time.

Ms Gregory said if the matter was sent back to the District Court or the Children's Court for a retrial, the Commonwealth would seek a discontinuance given the policy not to prosecute juveniles in people smuggling cases.

Compensation on the cards if conviction quashed

If the conviction is overturned it could open the Federal Government up to compensation claims.

Mr Jasmin was released in 2012, after extensive media coverage of his case, and deported to Indonesia.

In July 2014, his lawyers applied for their client to have the right to appeal against his people smuggling conviction.

The decision sat with Attorney-General George Brandis for more than a year.

Mr Jasmin's lawyers then took the case to the Federal Court in an attempt to force Mr Brandis to make a decision.

In November 2015, Mr Brandis acknowledged doubt about the reliability of the wrist X-ray to determine Mr Jasmin's age raised an issue that should be dealt with by courts and referred the matter to the WA Court of Appeal.

The court today reserved its judgement in the matter.