Gary McKinnon, who hacked into US military computers, will suffer psychologically if imprisoned there, his lawyers say

“Humanitarian considerations” that have arisen in the case of Asperger’s syndrome sufferer Gary McKinnon mean he should not face trial in the US for hacking into American military computers, the high court heard today.

In a last-ditch attempt to overturn earlier court decisions that the 43-year-old “UFO enthusiast” should be extradited, his lawyers accused prosecutors of ignoring the “disastrous consequences” of facing trial and a possible lengthy prison sentence in an American “supermax” prison.

The case also comes as the Tories are expected to devote an opposition day debate in parliament tomorrow to McKinnons’ extradition, after David Cameron said he was “deeply saddened and worried” about the case.

McKinnon’s barrister, Ed Fitzgerald, told the high court: “The Crown Prosecution Service wrongly failed to address the specific human rights issues, and the humanitarian issue, raised by the claimant’s Aspergers syndrome.

“The CPS, as a public authority, had a duty to consider whether its failure to prosecute [in the UK] has inevitably exposed him to an avoidable and unnecessary risk of serious psychological suffering,” he added.

The hearing comes after McKinnon signed a statement earlier this year admitting he had committed an offence under UK law by hacking into 97 computers belonging to the US navy and Nasa. The incident, which the US government says is the “biggest military hack of all time” and cost more than $700,000 (£430,000) in repairs, has led to talks between UK prosecutors and the US department of justice since charges were originally brought against the 43-year-old in New Jersey in 2002.

Although previous attempts to halt the extradition – which reached the House of Lords last year – failed, McKinnon’s lawyers have since obtained a diagnosis of Asperger’s syndrome after consulting two psychiatrists last year.

“Both experts referred to the grave risk to his health if he was extradited to the US, and [autism expert] Professor [Simon] Baron-Cohen referred to the risk to his life,” Fitzgerald said. “[The director of public prosecutions] failed to confront the human rights arguments for prosecutions in this country rather than in the US,” Fitzgerald added.

Both former home secretary Jacqui Smith and the current home secretary, Alan Johnson, have said they would comply with US requests for McKinnon’s extradition, while prosecutors argue that although McKinnon has admitted to “computer misuse” under UK law, it is less serious than the offence of “computer fraud” alleged against him in the US

The CPS, which defended its positiontoday , claims that the damage caused by the offence took place in the US, and that the investigation and most of the witnesses and evidence were located there. In February the director of public prosecutions, Keir Starmer, said there was not enough evidence to try McKinnon in the UK, an argument which McKinnon’s lawyers deny.

“This was inconsistent with the CPS’s own finding that there was sufficient evidence to prosecute,” Fitzgerald said. “McKinnon’s computer hacking conduct all took place in the UK, insofar as he was located here and using a computer in his home in the UK when he gained unauthorised access to the US systems.”

McKinnon, from Wood Green, north London, is described as “vulnerable” and “misguided” by his supporters, who contrast the efforts to extradite him with terrorist suspects who have been kept in the UK.

“I will not give up this fight until the government intervenes to protect my vulnerable son,” McKinnon’s mother, Janis Sharp, said. “When considering the extradition of Abu Hamza, the then home secretary said ‘Had we evidence in this country of a crime committed here then of course the police and the attorney general would have taken action’. Well, if that’s the approach for a convicted terrorist, why not for a gentle, misguided Asperger’s sufferer like Gary?”