He went by the name of Solo, using a home computer to allegedly hack into highly sensitive military sites to prove that UFOs do exist.

By his own admission he was a "bumbling computer nerd" whose obsession with breaking into some of the most important defence networks in the world got out of control. So involved was he with his mission, he stopped washing and rarely changed out of his dressing gown. Gary McKinnon was eventually thrown out of the north London home of his girlfriend from where he launched his adventures into deep cyberspace.

Yesterday, the price for his obsession became a lot higher, when the House of Lords decided that he should be extradited to the US to stand trial on charges that he posed a risk to national security after bringing down parts of the US Army security network.

He could now face a 70-year jail sentence and a £1.7m fine. There have been fears that he could be detained at Guantanamo Bay, but the UK justice system has sought assurances that this will not be the case.

Mr McKinnon was first arrested in 2002, not long after leaving an anti-war message, signed by Solo, on one of the networks which he hacked into. He has always denied he was a terrorist. Mr McKinnon believes the US military has reverse engineered an anti-gravity propulsion system from recovered alien spacecraft, and that this propulsion system is being kept a secret.

The House of Lords decision will make Mr McKinnon the 40th British citizen to be surrendered to the US under the 2004 Extradition Act, which was drawn up with no consultation of parliament and approved using Royal Perogative rules which allow changes in legislation to be voted through by a Commons committee.

The law has been heavily criticised given that the US can request extradition on the basis of identification alone, and without the need for evidence that a person has been responsible for a crime.

Mr McKinnon has been given 14 days to fight for his right to stay in Britain through the European Court of Human Rights.

The Law Lords said that the seriousness of the allegations meant that extradition was inevitable, but Mr McKinnon's legal team argue that the US want to make an example of the man who broke into their military networks, at a time of an international security crisis, with relative ease.