The man whose evidence convicted corrupt former Met Police commander Ali Dizaei says he has been "betrayed" by Britain after his deportation ruling.
The Home Office said Waad al-Baghdadi should be deported after lying about his age when he came to the UK.
Mr al-Baghdadi was previously asked to testify against the ex-Scotland Yard senior officer in two trials.
Dizaei falsely accused Mr al-Baghdadi of assault and then arrested him.
A former commissioner at the Independent Police Complaints Commission (IPCC) has said it would be "an appalling injustice" if the witness is deported.
Mr al-Baghdadi has now claimed asylum - saying he fears for his life if deported to either Iraq or Iran.
Mr Dizaei told the BBC: "Waad al Baghdadi's lies about his immigration status alarmed the public, including my friends, family and associates, who wrote to their MPs of their own accord."
He went on to say if his wife had not reported al-Baghdadi, he "would probably still be claiming the benefits today".
The case began in 2008, by which point Dizaei's bosses had already spent up to £7m investigating him for alleged corruption.
In a Kensington restaurant one summer evening, Dizaei got into an argument with a young web designer who was asking to be paid.
But Dizaei didn't pay him - instead he arrested him and called 999 for urgent back-up.
But the only crime committed that evening was by Dizaei. He inflicted injuries on himself to try to frame an innocent man.
That man was Mr al-Baghdadi. His evidence was crucial in jailing Dizaei. But now, eight years on, he is being thrown out of the country because he lied about his age to get in.
Mr al-Baghdadi said: "I knew there were some bad things about me I've done in the past.
"I knew if I testified against Ali Dizaei these might come to the light. But I chose to do the right thing."
He said British authorities knew he had lied about his past and that he was a benefits cheat - but were still happy to use him as the key witness to convict Dizaei.
He says now they have betrayed him.
Mr al-Baghdadi added: "They used me. They held a gun against Ali Dizaei and I was the bullet. So my life was destroyed.
"I sacrificed my life. Not in one trial but in two trials."
The first of the two trials happened in 2010, when a jury believed Mr al-Baghdadi's evidence that he had been framed by Dizaei.
Dizaei was jailed.
But the following year the verdict was overturned when a retrial was ordered after it emerged Mr al-Baghdadi had lied about his personal details and had claimed £27,000 benefits on behalf of his late father.
And Mr al-Baghdadi was jailed.
However, the following year, just weeks after he had been released, the prosecution asked him to be their main witness once again.
A second jury again believed him - and Dizaei was jailed once more.
In 2012, a commissioner at the IPCC, Deborah Glass, said: "If that great power is abused by any police officer, it is vital they be held to account for it:"
Ms Glass has since left the IPCC. She said: "Mr al-Baghdadi had nothing to gain by pursuing a complaint against Ali Dizaei - except justice.
"The kind of courage he showed in giving evidence is fundamental to bringing corrupt officials to account.
"If this man is deported as a direct result of his challenging a powerful and corrupt police officer, that would be a most appalling injustice."
Mr al-Baghdadi said what happened at the Kensington restaurant back in 2008 has ruined his life - he claims ever since he decided to stand up to Ali Dizaei, he has faced a campaign against him.
Numerous allegations have been made against the man - including rape - but he was never charged.
Documents submitted to an Immigration Tribunal reveal seven letters were written to the government asking about al-Baghdadi's immigration status.
In them, the IPCC said: "There is intelligence held by the IPCC which links the authors of all of these letters to Mr Dizaei."
They also refer to a tip-off to the authorities that al-Baghdadi had committed benefit fraud.
The IPCC found: "It was established that the person who had originally made the anonymous allegations to the DWP was the second wife of Mr Dizaei."
A spokesman for the Home Office said it would not comment on ongoing legal proceedings, but added: "When someone is found to no longer need our protection, we expect them to leave the country voluntarily.
"Where they do not, we will seek to enforce their departure."