The Home Secretary Theresa May announced today that she would block Gary McKinnon's extradition to the US where he is accused of hacking into military computers.
Speaking in the House of Commons, Mrs May said he was accused of "serious crimes" but that there was strong evidence to suggest he would try to kill himself if extradited.
She said it was now for the Director of Public Prosecutions, Keir Starmer QC, to decide whether Mr McKinnon should face trial in the UK.
Mrs May said her decision was based on medical advice from a range of practitioners recommended to her by the Chief Medical Officer, as well as extensive legal advice.
ITV News Correspondent Juliet Bremner reports:
McKinnon's mother Janis Sharp, who has campaigned for her son to face justice in the UK, thanked the Home Secretary for her decision.
"Thank you Theresa May from the bottom of my heart - I always knew you had the strength and courage to do the right thing," she said.
She added her son "literally couldn't speak" following the news and had cried and hugged her.
The decision was also welcomed by McKinnon's MP, David Burrowes, who had vowed to resign if his constituent was sent to the US to face justice.
He said it represented a "victory for compassion and pre-election promises being kept".
Mrs May also said she would introduce the so-called 'forum bar' which will give British courts greater discretion to decide whether people should face trial in the UK or in the country where the extradition request originates.
Mrs May also said the Government will review a range of extradition agreements with other countries, including the European Arrest Warrant.
That triggered three successive applications for judicial review and questions about the fairness of the extradition treaty this country shares with the US.
US authorities accuse Mr McKinnon of hacking into dozens of US military computers between 1999 and 2002 from his home. He could have faced 60 years in jail if convicted in the US.
Mr McKinnon - who suffers from Asperger's syndrome - admits hacking into the computers but claims he was looking for evidence of UFOs.
The US Department of Justice said the United States "is disappointed by the UK Home Secretary's decision not to extradite Gary McKinnon, particularly given the past decisions of the UK courts and prior home secretaries that he should face trial in the United States".
"We note that the Home Secretary has described this case as exceptional and, thus, this decision does not set a precedent for future cases," a spokesperson added