In opposition, both the Conservative and Liberal Democrat party leaders had argued forcefully that Gary McKinnon should stand trial in Britain rather than America for breaking into military networks.

Mr Cameron had said he was "deeply saddened and worried" about the case and claimed there was "no compassion" in sending a "vulnerable young man" thousands of miles away from his family, to serve up to 60 years in prison.

Mr Clegg called the Labour government's decision to extradite Mr McKinnon a "disgrace" and a "hammer blow to British justice".

In opposition Chris Grayling, now Justice Secretary; Dominic Grieve, now the Attorney General; and James Brokenshire, now the Security Minister, also expressed support for Mr McKinnon in his lengthy fight against extradition.

But although Theresa May ordered a review of the medical evidence soon after the general election in 2010, the threat of deportation has continued to loom over Mr McKinnon and his family.

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On Tuesday, more than 10 years since he was first arrested by British police over the "biggest military computer hack of all time", Mr McKinnon will finally learn his fate.

The Home Secretary will announce to the House of Commons the long-awaited decision on his extradition, as well as the Government's response to an independent review of the treaty with the US following claims it is "one-sided".

Mr McKinnon's lawyer said on the eve of the ruling that she hoped the Prime Minister and his deputy would honour the promises they made previously.

Karen Todner said: "It has been a long 11-year battle to fight this extradition and we wait with anxiety, but hope, that the Home Secretary will uphold the promises previously made by Mr Cameron and Mr Clegg.

"We hope that our elected Government will uphold the promises they made whilst in Opposition and will prevent Mr McKinnon's extradition to America."

She added that psychiatrists instructed by the Home Office agree that Mr McKinnon, who has Asperger's Syndrome, would be at high risk of attempting suicide if he were transferred to the US for trial.

His mother, Janis Sharp, said her son, now 46, had spent the past decade in a "zombified" state with the threat of jail in a foreign country hanging over him, and banned from going online. Mr McKinnon admits hacking into Pentagon networks but says he was only trying to find evidence for the existence of UFOs.

Mrs Sharp said the new medical reports had raised her hopes that her son might win a last-minute reprieve, but she remained scared of what might happen.

Asked about the former support of senior politicians, she said: "People like this would not use Gary's case as a key part of an election campaign and then leave him for two-and-a-half years and then throw him to the wolves.

"It would seriously damage their reputations in terms of honesty and integrity.

"I will respect him (Mr Cameron) when I know Theresa May and David Cameron have the strength to say no."

Lawyers for Mr McKinnon, who lives in Palmers Green, north London, may try a last-ditch application for judicial review in November if extradition is approved.

Experts say the case should prompt the Government to change the current system by including a test of which would be the fairest jurisdiction in which to hold a trial.

Michael Caplan, QC, an extradition specialist at Kingsley Napley LLP, said: "It should be for a British judge to hear all the arguments in favour of domestic prosecution and balance those against the requesting country's application for extradition.

"He will have in mind where most of the conduct took place and where the trial should take place in the interests of justice.

"A forum test could prevent the delays and controversies we have seen in recent extradition cases."