A British computer hacker accused by the United States of breaking into top secret military and space agency networks will learn the result of his six-year fight against extradition within three months, a court heard on Tuesday.

Gary McKinnon faces up to 60 years in jail if convicted in American courts for what one U.S. prosecutor has described as the "biggest military computer hack of all time".

U.S. officials say he knocked out hundreds of military computers in the months after the September 11, 2001 attacks, undermining security and causing damage worth nearly $1 million.

McKinnon, 46, admits hacking into Pentagon and NASA computers from his bedroom in London, but says he was only looking for evidence of aliens and UFOs.

He suffers from Asperger's syndrome, a form of autism, and his lawyers say he is too ill to be sent for trial in the United States.

British Home Secretary (interior minister) Theresa May will announce her decision on whether McKinnon should be sent to the United States for trial by mid-October, a lawyer representing the British government told the High Court in London.

May has been studying medical reports before making up her mind and has been busy supervising the security for the Olympic Games, which open in London on Friday. Her spokesman had no immediate comment on the case.

McKinnon's mother Janis Sharp said the further delay was unacceptable.

"If Theresa May had got an ounce of compassion she would make her decision now, before the Olympics, because she has any number of medical reports - these delays are destroying my son's life," she told reporters outside court.

Campaigners have urged the British government to do more to help McKinnon, who was first arrested in 2005. Prime Minister David Cameron and President Barack Obama have discussed the case.

McKinnon's supporters say his case shows that an extradition treaty signed by Washington and London after the 9/11 attacks is unfair and biased against British criminal suspects.

A committee of British lawmakers came to the same conclusion, saying in March that the treaty was unbalanced and made it easier to extradite a British citizen to the United States than vice versa.

However, a judge-led review ordered by the British government concluded last October that the extradition treaty was fair, with "no practical difference" between the evidence each country needs to provide to seek a suspect's transfer.