He insists he hacked into the computer networks only to find evidence of extra-terrestrial landings. He is self-taught and worked under the name Solo but managed to cause more than £475,000 ($990,660) in damage to some of the most supposedly secure computers in the US, including those operated by NASA, the Pentagon and several arms of the US military.

The House of Lords was told McKinnon should not be extradited to the US because US prosecutors attempted to intimidate him into co-operating with them. They were told that, if the extradition was allowed to go ahead, he would become a victim of abuse of process. In an interview posted on YouTube, McKinnon insists the only reason he was able to gain computer access to the networks was because they were badly protected by lax security.

In 2005, McKinnon made world headlines when British prosecutors described his hacking exercise as one of the biggest ever military computer breaches. He did the work from a room in his girlfriend's aunt's house in North London. McKinnon was taken into custody when he was discovered in 2002 but was never charged in Britain. Last year, he lost an appeal in the High Court to stop his extradition to the US.

His lawyer, David Pannick, QC, told the House of Lords that McKinnon had been told by US authorities that, unless he agreed to plead guilty to an extradition he would face an even tougher sentence. Reports on the internet have also quoted a US embassy legal official who said New Jersey authorities said they wanted McKinnon to "fry". Mr Pannick told the Lords it had the power to turn down an extradition if it believed there was an abuse of process.

"The US prosecutors sought to impose pressure on the appellant through his legal advisers to consent to extradition and plead guilty," he said. He said one threat had been to treat the case as a terrorism case with a potential 60-year jail term on the cards.



McKinnon was told, on the one hand, that if he co-operated he would receive a jail sentence of between 37 and 46 months with a possible repatriation to Britain after half the time.

"By contrast, the appellant's representatives were told that if the appellant declined to co-operate, this sentence would be in the region of eight to 10 years, possibly longer," Pannick said. The Guardian reported yesterday that a judgment is expected within three weeks.