A soldier who has been deemed a suicide risk said the Government had sounded his "death knell" by deciding his extradition to the United States over fraud charges must go ahead.
David McIntyre, 42, who served in Afghanistan, was given additional time by Home Secretary Theresa May to provide proof that he was suffering from an untreated post-traumatic stress disorder (PTSD).
But despite providing further medical evidence, McIntyre, who remains a reservist soldier, has been told he must be removed to the US.
Now living in Worsley, Greater Manchester, McIntyre, 42, said: "I'm really disappointed by the decision.
"I can't put it into words.
"It's like a death knell."
His lawyer Karen Todner, of Kaim Todner solicitors, confirmed the Home Secretary's decision and said her firm was going to consider whether it could seek judicial review.
The Americans have accused McIntyre, who served with the Queen's Lancashire Regiment and Royal Military Police, of overcharging a US peace group for a security contract when he was running his own firm - charges he denies.
McIntyre, who faces a 20-year jail sentence if he is extradited to the US, served in the Territorial Army before joining the Queen's Lancashire Regiment in 1996.
He said he feared his removal could be imminent.
"I'm always the last to know, " he said.
"The Home Secretary could turn around and say 'He is going in two days'.
"That's really worrying me."
McIntyre left the Army in 2002 and set up security company Quantum Risk, which employed a team of 20 to provide security to American clients, including the Iraqi ambassador to the US.
The business closed in 2009 and McIntyre enrolled in the Royal Military Police, for whom he served in Afghanistan.
It was last July when the US charges emerged and the soldier was flown back from Camp Bastion, in Helmand Province, to face extradition proceedings.
McIntyre faces eight counts of fraud concerning a contract with the United States Institute of Peace (USIP).
It is alleged he overcharged the organisation by 100,000 US dollars (£65,000).
He said: "There's no substance and I completely deny everything.
"I've never said I'm not prepared to stand in the dock - but to do it in the US, I know how they work."
McIntyre said in the US he would be told to "cough to something he hasn't done" and sign a so-called plea bargain to ensure a short sentence or face never coming home.
"They're looking to give me 20 years," he said.
"The Home Secretary in all her wisdom has decided anything I've ever done for my country is completely defunct."
McIntyre said he does not want to be treated differently because he is a soldier but added that he would like his "last 20 years in uniform to have counted for something".
He added: "I can't fight the US on my own."
His appeal was dismissed in February before he had presented the court with a report from the British Army's consultant psychiatrist confirming that he suffers from PTSD and warning that if he is extradited he could react "impulsively, dangerously and potentially tragically".
McIntyre's legal team, which also represented Gary McKinnon, the so-called "hacker" whose extradition to the US was blocked by the Government, submitted further medical evidence to the Home Office - but to no avail.
The former soldier believes he is the victim of a plea bargain in which a US official, accused of similar offences, named him to secure a lenient sentence.
McIntyre said he had been suffering from the severe anxiety disorder for many years but kept it private.
He said the extradition proceedings had worsened the condition and brought it to the fore.
Melanie Riley, campaigner with Friends Extradited, said: "Here's yet another vulnerable British soldier let down by his own government.
"Dave was prepared to give his life in the defence of his country. Yet when Dave needed his country to defend him from extradition to the US, they booked him the flight.
"If he has a case to answer, let him answer it in the UK, where his mental health can be properly treated and where he can be surrounded by the loving support of his partner, family and friends, not locked up in a cell 5,000 miles from home while he tries to clear his name.
"Case after case demonstrates the cruelty of extradition which should be the last resort, not first, in our fight against alleged crime."
A Home Office spokeswoman said: "On March 22 the Court of Appeal rejected David McIntyre's appeal against extradition and he was refused leave to appeal to the Supreme Court.
"We agreed to suspend extradition pending further representations to the Secretary of State from McIntyre's solicitors.
"These representations have been carefully considered and it has been decided that proceeding with extradition would not breach his human rights."