So, British Home Secretary Alan Johnson is to celebrate the lopsided “special relationship” by offering the Americans a Thanksgiving gift they have wanted for years: a brilliant but delusional computer geek who believes in little green men.

Glasgow-born Gary McKinnon, 42, is a fantasist, not a terrorist. He should not be put in prison. Yet unless he is saved by a judicial review of his case, and if he refuses a plea bargain, the arbitrary nature of American justice is such that he faces up to 60 years in a maximum security jail.

This case raises two important issues: the asymmetric extradition arrangements between Britain and the US, and the way the justice system treats the mentally ill. His misfortune is that he chose to hack into US government computers in 2001 in his obsessive search for UFOs. In the febrile atmosphere following the Twin Towers attacks, Britain passed legislation to facilitate the extradition of terrorists. It allows British citizens to be seized on the basis of a warrant, while to bring an American to Britain, the authorities here must demonstrate they have a good case. Mr McKinnon admits computer misuse, which in Britain carries a maximum sentence of five years, but denies what the Americans describe as “the biggest military hack of all time” or causing $700,000 (£425,000) of damage. The government’s own adviser on terrorism legislation, Lord Carlile, has described the extradition as “disproportionate, unnecessary and avoidable”. He should be tried here. If the Home Secretary has as little discretion as he claims in this, then the law requires reform.

Mr McKinnon has Asperger’s syndrome, which explains his obsession and disregard for the consequences of his actions. The American justice system is a byword for the maltreatment of the mentally ill, and US assurances about his treatment count for little. His mother, Janis Sharp, who has mounted a determined and eloquent campaign on his behalf, believes extradition would cost him his life.

Embarrassed by the ease with which this computer wizard

penetrated their systems, the US authorities want to make an example of him. They would be better off picking his extraordinary brain. There is potential for tragedy here, in which case Alan Johnson would have blood on his hands. The fight for Gary McKinnon must go on.