A Scottish man facing extradition to the United States to stand trial for a murder in Florida has began a High Court bid to avoid facing the American justice system.

Phillip Harkins, originally from Greenock, Renfrewshire, is accused of shooting dead 22-year-old Joshua Hayes during a botched robbery in Jacksonville, Florida, in August 1999.

He was arrested and charged, but returned to Scotland where he was jailed in 2003 for killing a grandmother in a car crash in his home town. The 32-year-old Scot, who had been living in the US at the time of Mr Hayes' death, challenged a decision by the Home Office to grant his extradition to stand trial.

His legal team, led by David Hislop QC, argued that his extradition would violate his human right not to be subjected to "inhuman or degrading treatment".

Mr Hislop said: "We say that, if extradited, this claimant is in real risk of suffering a sentence that, in our respectful submission, would be grossly disproportionate." Mr Harkins, who has three young children, is accused of killing Mr Hayes when his gun accidentally went off, hitting the young dad in the head.

If convicted, he faces a mandatory sentence of life imprisonment, without the possibility of parole at any time, the barrister told Lord Justice Gross and Mr Justice Davis.

"We say that, taken at its highest, the case would seem to be of an accidental killing, albeit in the course of a robbery," he continued.

"If that is right, then we say there is a real risk that, in the particular circumstances of his case, if he is in receipt of a sentence of life without parole, then that sentence would most surely be grossly disproportionate."

Although several other prisoners had had sentences commuted, they had all committed their crimes before the law in Florida was changed in 1994, he said.

The United States Government is contesting Mr Harkins' challenge. The High Court hearing continues.