The US authorities are so desperate to extradite my son that they have changed the law. Now he faces 60 years in jail

Any day now, my son, Gary McKinnon, could face extradition from Britain to the United States, where he would stand trial for hacking into US government computers and could face a sentence of up to 60 years.

Gary has recently been diagnosed with Asperger's syndrome, which is why I and his family and his many friends and supporters around the world are arguing that he should be allowed to stay in the UK and face the courts in the country where the offence – if offence there was – was committed.

The US authorities waited two years to call for Gary's arrest because of a then-unratified, unsigned extradition treaty between the two countries, which would make it easier for them to have a British citizen sent for trial in the US. Yet, when he was first arrested in London, six years ago now, Gary was told he would probably get a sentence of community service for his hacking activities.

He naively admitted computer misuse before he had engaged a lawyer and without a lawyer even being present. We were still unaware at that time that he had Asperger's syndrome.

Gary gained no leniency for his honesty and on the contrary, his extradition has been relentlessly pursued by the British and American authorities, despite the Crown Prosecution Service (CPS) declining to prosecute him in Britain. This attitude will hardly encourage British citizens to come clean regarding any crimes they may have committed. If no leniency or consideration is given when a person accused of a crime immediately and openly tells the truth, there is little point in them admitting to anything.

The CPS's decision not to prosecute Gary here was clearly made to allow the Americans to arrest him two-and-a-half years later, once the one-sided extradition treaty was introduced and then made retrospective.

In addition, in order to indict Gary, the US authorities had to claim a specific amount of financial damage. Gary has always denied causing damage and without proof of such, the US could not prosecute him. Just a month ago the US prosecutors stated in an interview that once Gary was extradited, the most difficult thing to prove would be the damage!

Several weeks ago the goalposts were moved yet again when the US introduced a new law whereby no proof of damage was required where military computers were concerned. For the American law to then have been conveniently changed at such a crucial time does little to give us any faith in such a legal system.

There is a London demonstration outside the US embassy, scheduled for 4pm on September 28 in Grosvenor Square. See the campaign website for more details.