GARY McKINNON felt he had become a "dead person" during his 10-year battle against extradition to America for computer hacking but now believes he has the chance to lead a normal life again, his tearful mother Janis Sharp said.

Ms Sharp explained how her 46-year-old son reacted to the landmark decision by Theresa May, in which the Home Secretary did something her three Labour predecessors had failed to do – defy the US authorities and stop an extradition, using the Human Rights Act.

"He couldn't speak. He cried and then he hugged. There's been hugging and crying. It's so emotional," said Ms Sharp as a wall of cameras repeatedly clicked at her every movement behind the microphone.

She gave an insight into how her son – who suffers from Asperger's Syndrome, a form of autism – had coped with what she described as the "emotional rollercoaster" of the past 10 years.

She said: "He felt he was dead; he had no job, he had no children. He doesn't leave the house. He has no conversation. He has nothing. He felt he was worthless."

Ms Sharp was in tears as she described her son's "horrendous" decade-long ordeal. He would, she explained, "just sit in the dark all the time".

"You saw him shut down and slow down," she added. "It's been awful watching Gary go downhill so badly, but such a relief to watch him smile for the first time in many years. It's amazing."

Ms Sharp left no doubt that if the decision had gone the other way, her son would have taken his own life.

"It's been a life-saving decision. Gary doesn't travel abroad. He rarely leaves London. To take him from everything he knows, several thousand miles away, is so terrifying to him. I can understand he felt he would rather be dead," she said.

She thanked her son's legal team, the media, human rights campaigners and a host of celebrities, including actresses Julie Christie and Trudie Styler as well as musicians David Gilmour and Bob Geldof.

She said: "Without people power of all these different people together there's no way Gary would have stayed here."

Earlier at Westminster, the Home Secretary told MPs how Mr McKinnon was accused of serious crimes, yet there was no doubt he was seriously ill.

It is alleged he hacked into US Navy computers in the wake of the 9/11 terror attacks, disabling hundreds of systems. He admits accessing them but claims it was to search for evidence of UFOs.

Ms May explained how she had considered representations on the accused's behalf, including from a number of clinicians. She also got her own expert medical and legal advice.

She said: "After careful consideration of all of the relevant material, I have concluded Mr McKinnon's extradition would give rise to such a high risk of him ending his life that a decision to extradite would be incompatible with his human rights. I have therefore withdrawn the extradition order against him."

Some MPs applauded and cheered. David Burrowes, the accused's local MP in London, said it had been a "victory for compassion".

The computer hacker was arrested in 2002 and then again in 2005 before an order for his extradition to America was made in July 2006.

This triggered three successive applications for judicial review and questions about the fairness of the UK-US extradition treaty, which critics claim is one-sided. An independent review of the UK's extradition arrangements last year found the current transatlantic treaty was "balanced and fair".

Mrs May said the Government accepted the review's recommendations, but would look to create a so-called "forum bar", where extradition cases would be heard in an open court before any decisions were taken.

She explained in future it would not be up to home secretaries to hear appeals on human rights grounds but the court.

Yvette Cooper, her Labour Shadow, said she was worried the decision could make it easier for others with less clear-cut cases to try to avoid extradition.

Tory MP David Davies insisted Mrs May had "stood up for the rights of British nationals and for the wider British national interest".

However, Alan Johnson, the former Labour Home Secretary, criticised the decision and claimed Mrs May had made a decision which was "in her own party's best interests but it's not in the best interests of this country".

Last night, a spokeswoman for the US State Department said it was "disappointed by the decision to deny Gary McKinnon's extradition to face long overdue justice in the United States" and would be "examining the details of the decision".

Keir Starmer, Director of Public Prosecutions in England, now has to decide whether Mr McKinnon should face trial in Britain.