Gary McKinnon could face a prison sentence of 45 years

Glasgow-born Gary McKinnon, of north London, is accused of gaining access to 97 US military and Nasa computers.

Home Secretary John Reid granted the US request to extradite him for trial.

At the High Court in London, his lawyers argued the 41-year-old had been subjected to "improper threats" and the move would breach his human rights.

His lawyers had argued that, if extradited, he would face an unknown length of time in pre-trial detention, with no likelihood of bail.

He would also face a long prison sentence - "in the region of 45 years" - and may not be allowed to serve part of the sentence at home in the UK, his lawyers had said.

But, on Tuesday, Lord Justice Maurice Kay and Mr Justice Goldring dismissed his legal challenge, saying they could not find any grounds for appeal.

We will certainly be applying for this court to certify a point of law of public importance and to grant leave

Ben Cooper

Representing Gary McKinnon

Profile: Gary McKinnon

Ben Cooper, for Mr McKinnon, said his client would now seek to make an appeal against his extradition at the House of Lords.

"We will certainly be applying for this court to certify a point of law of public importance and to grant leave," he said.

Speaking later, solicitor Jeffrey Anderson said alleged threats by US authorities, including one from New Jersey prosecutors that Mr McKinnon "would fry", would be among issues raised.

That had been a "chilling and intimidating" reference to capital punishment by the electric chair, he added.

It now looked as though the US would try to prosecute Mr McKinnon as a cyber-terrorist, Mr Anderson said.

"This could lead to him spending the rest of his life in prison in the US, with repatriation to serve his sentence in his home country denied as punishment for contesting his extradition."

Mr McKinnon has never denied that he accessed the computer networks of a wide number of US military institutions between February 2001 and March 2002.

Mr McKinnon, arrested in November 2002, has always maintained that he was motivated by curiosity and that he only managed to get into the networks because of lax security.