The son of Australia's most notorious bank robber and prison escapee says it's time to set his father free. 

Brenden Abbott, known as the "Postcard Bandit", has launched a Supreme Court challenge to his Western Australian jail term, 36 years after he broke out of Fremantle Prison.

His son, James Laycock, who he fathered while on the run, flew from Sydney to attend the hearing. 

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"Having my father around would be great. Haven't had it before. So wait to see what happens," said Laycock.

Abbott gained notoriety for a series of jailbreaks and robberies across Australia, beginning with his 1989 escape from Fremantle Prison.

He was captured in Queensland six years later, only to escape custody again. 

The law finally caught up with him in 1998, when he was arrested in Darwin. 

Abbott has been locked up ever since, serving 18 years in Queensland before being extradited to Perth in 2016 to finish his original robbery sentence. 

He's now served more time than some murderers. 

"Doing crimes, you get jail time for doing the wrong thing, but it's been way too long," said Laycock.

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Abbott's lawyer, Matthew Crowley, is now fighting the legality of his ongoing imprisonment in WA, telling a court "there's a complicated patchwork at play".

Mr Crowley says his client's 1980s robbery sentence kept running while he was at large, expiring in 1994 – meaning by the time he was caught, he'd "achieved an unconditional right of liberty". 

The case is incredibly complex, but much of it centres on what sentencing laws applied at the time of Abbott's escape and recapture. 

The now-63-year-old is eligible for parole in October of next year. 

If he wins this case, he could be freed sooner. 

The hearing has been adjourned until next month.

This article was produced with the assistance of 9ExPress.