Alleged computer hacker Lauri Love is beginning a High Court challenge against his extradition to the US.
Authorities in America have been fighting for Mr Love, who has Asperger syndrome, to face trial on charges of cyber-hacking, which lawyers have said could mean a sentence of up to 99 years in prison if he is found guilty.
The Lord Chief Justice Lord Burnett and Mr Justice Ouseley will hear the action over two days in London, beginning on Wednesday.
The 32-year-old, who lives with his parents near Newmarket in Suffolk, is alleged to have stolen huge amounts of data from US agencies, including the Federal Reserve, the US Army, the Department of Defence, Nasa and the FBI in a spate of online attacks in 2012 and 2013.
In September 2016 a district judge at Westminster Magistrates’ Court ruled that Mr Love could be extradited.
Home Secretary Amber Rudd authorised Mr Love’s extradition to the US in November 2016 and a Home Office statement said at the time that she had “carefully considered all relevant matters”.
Mr Love’s supporters have accused Prime Minister Theresa May of failing to raise the case with Donald Trump in the hope he would intervene and order US authorities to allow him to be tried in the UK.
And a cross-party group of 73 MPs warned recently that there was a “great probability” that Mr Love would end his own life if sent to the US.
In a letter to Attorney General Jeremy Wright, the MPs said “eminent experts” judged Mr Love would be at “very high” risk of suicide if sent to the US and urged him to pass on their concerns to his American counterparts.
Their warnings echoed worries raised in October 2016, when more than 100 MPs wrote to then-president Barack Obama calling on him to block the extradition, stressing their “deep concern” for Mr Love’s safety.
His case bears similarities with that of Gary McKinnon, another alleged cyber-hacker with Asperger syndrome, who eventually had his extradition blocked by Mrs May in 2012, when she was home secretary, after a decade-long legal battle.
However Mrs May later announced changes to the law that transferred powers in extradition cases away from the Home Secretary to the courts.
Further changes introduced in 2013 allow judges to block extradition if a “substantial measure” of the alleged offence took place in the UK and extradition would not be in the interest of justice, known as the forum bar.
The Courage Foundation, which runs Mr Love’s defence fund and support campaign, says his case “raises concerns about Britain’s willingness to extradite vulnerable citizens to face potential life-long jail terms in conditions far worse than would be countenanced domestically”.
The High Court challenge centres on the extradition ruling made by District Judge Nina Tempia.
Mr Love’s legal team will argue she did not consider the forum bar issue correctly and that extradition would not be compatible with Mr Love’s human rights, particularly in relation to protection from inhuman and degrading treatment and his right to a private and family life.