Scottish computer expert Gary McKinnon today lost his latest High Court bid to avoid extradition to America where he faces trial for hacking into US military networks.

His lawyers argued that extraditing the 43-year-old, who suffers from Asperger's Syndrome, would lead to "disastrous consequences" for his health, including possible psychosis and suicide But today Lord Justice Stanley Burnton and Mr Justice Wilkie, sitting in London, dismissed his claim for judicial review.

Mr McKinnon, from Wood Green, north London, asked the court to overturn decisions of successive Home Secretaries allowing his extradition to go ahead.

He also challenged a refusal by Keir Starmer QC, the Director of Public Prosecutions (DPP), to put him on trial in the UK on charges of computer misuse. A UK trial would allow him to avoid extradition.

Lord Justice Burnton said: "For the reasons set out in the judgment the claims against the secretary of state and DPP are dismissed."

Lawyers for Mr McKinnon, who was told the decision yesterday, described him as a "UFO eccentric" who had been searching for evidence of extra-terrestrial life, and described the idea that he was a danger to US national security as "a complete fantasy".

The US authorities said Mr McKinnon was responsible for the "biggest military hack of all time" that had been highly damaging and involved 97 government computers belonging to organisations including the US Navy and Nasa.

A large campaign involving family, politicians, civil rights groups, sympathetic media and celebrities has supported the hacker's long battle against extradition.

His mother, Janis Sharp, has expressed fears that he could face a 60-year sentence in a tough US jail and she would never see him again.

Mr McKinnon was not in court today to hear the judgment.

But the National Autistic Society, which has supported him, said it was "extremely disappointed at the decision".

Amanda Batten, the charity's head of policy and campaigns, said outside the High Court: "We are angry that Gary is still in this position.

"This legal case has been going on for seven years. We are involved in supporting his case because we think that in the light of his Asperger's Syndrome that extradition should not go ahead.

"We will continue campaigning and do all we can to support Gary to stay in the UK."

In a 41-page judgment, the judges ruled extradition was "a lawful and proportionate response to his offending".

Outside court Mrs Sharp said: "We are heartbroken. If the law says it's fair to destroy someone's life in this way then it's a bad law."

Whether or not Mr McKinnon can appeal further will be decided at a later date.

Lord Justice Burnton said it was a matter that should be dealt with "as expeditiously as possible", probably in September.

Mrs Sharp added: "Our hope still lies with the Government.

"What more evidence do Gordon Brown and Alan Johnson need to understand what extraditing Gary would do to him, let alone us?

"Gary would not survive and I would never see my son again. All to oblige the Americans?

"If Gary's was such a dreadful crime, he should have been prosecuted and sentenced here years ago.

"Instead he's been left tortured by fear for seven years. Compassion can and must now prevail."

Karen Todner, Mr McKinnon's solicitor, said: "This ruling is hugely disappointing. But we shall not stop here.

"Alan Johnson still has the power to act. We have 28 days to review the judgment and will continue to explore every legal avenue until we achieve a just and proper result.

"The Government promised 'ample protection' of individuals' rights, but we have yet to see this in practice.

"Extradition without effective safeguards is a denial of justice for every UK citizen."

Former Home Secretary Jacqui Smith decided last October to order Mr McKinnon's removal following a request from the US prosecuting authorities after all his previous legal challenges failed.

The current Home Secretary, Alan Johnson, has insisted he has no power to demand the trial take place in the UK.

The DPP refused to order a UK trial, saying the bulk of the evidence was located in the US and Mr McKinnon's actions were directed against the US military infrastructure.

But the hacker's lawyers argued extradition was "unnecessary, avoidable and disproportionate" and had not taken place in other cases.

Dismissing the challenge as "unarguable", Lord Justice Burnton said: "The fact that different decisions were made by the DPP in other cases does not assist the claimant: other cases, different facts."

Mr McKinnon admitted breaking into the US military computers in 2001-2, during a period of heightened security in the wake of the September 11, 2001 attacks.

The US government alleges his conduct was intentional and calculated to influence and affect it by "intimidation and coercion". It says the cost of repair totalled more than 700,000 US dollars (£436,000).

Campaigners seeking to block his extradition say he acted through "naivety" as a result of Asperger's - a form of autism which leads to obsessive behaviour - and should not be considered a criminal.

Edward Fitzgerald QC, appearing for Mr McKinnon, accused the Home Secretary of failing to take account of uncontradicted medical evidence of the severe mental suffering that extradition would cause.

He described Mr McKinnon as "an eccentric person who has passionate views about UFOs".

If sent to the US, Mr McKinnon was likely to receive a substantial prison sentence of up to 12 years, possibly served in a Supermax prison used for high risk inmates, and was unlikely to be repatriated to serve his sentence.

The process of extradition, trial and serving his sentence would inevitably expose Mr McKinnon to "an avoidable and unnecessary risk of serious psychological suffering" with "all of the attendant disastrous consequences", said the QC.

Previously Mr McKinnon's case against extradition has been rejected on other grounds by a district judge, the High Court and then, in July last year, the House of Lords. The European Court of Human Rights in Strasbourg also refused to intervene.

He was caught as he tried to download a grainy black and white photograph which he believed was an alien spacecraft from a Nasa computer housed in the Johnson Space Centre in Houston, Texas.

He was easily traced by the authorities because he used his own email address.

He has always said he had no malicious intent but was looking for classified documents on UFOs which he believed the US authorities had suppressed.

He has signed a statement accepting his hacking constituted an offence under the UK's Computer Misuse Act 1990.

The case has also once more brought into focus the inequality of laws which enable the US to extradite UK citizens with comparative ease, while it is much harder for the UK authorities to secure the removal of wanted American citizens to these shores.

Human rights campaigner and former hostage Terry Waite has called on the US to drop the charges, saying: "No nation under the sun ought to convict an individual whose behaviour is occasioned by illness."

Actress and environmental campaigner Trudie Styler, wife of pop star Sting, who was present in court, said afterwards: "My heart goes out to Gary, Janis and all those who have fought so hard.

"Reason and common sense dictate that Gary's extradition would be abhorrent.

"We cannot let this be the end of the road. It is quite clear that Gary is a deeply vulnerable man, ill-equipped to cope with the trauma of extradition.

"I am determined to continue to press government to intervene in this blatant travesty of justice."

Shadow home secretary Chris Grayling said: "This is very disappointing news. People are right to be extremely concerned about our extradition arrangements.

"This is a case where there is a clear argument for it to be tried in this country, and our system should take health issues into account before considering deportation. I hope lessons will be learned."

Former Liberal Democrat leader Sir Menzies Campbell said: "This is a profoundly disappointing decision.

"The people who should hang their heads in shame are the members of the Government who negotiated an extradition treaty with the United States which places British citizens in a much weaker position than their American counterparts.

"If this was happening in America there would be a public outcry and Congress would be moving might and main to prevent it."