Former Scotland Yard commander Ali Dizaei won his appeal against his conviction for corruption today - but faces a new trial.
Lord Justice Hughes and two other judges at the Court of Appeal in London allowed the challenge brought by Dizaei, 48, who is serving a four-year jail sentence.
Dizaei was jailed in February last year after a trial at London's Southwark Crown Court.
He was not present for the ruling.
Lord Justice Hughes, sitting with Mr Justice Treacy and Mr Justice Cranston, said the court had been "driven to the conclusion" that his conviction "cannot be regarded as safe".
They said: "We are satisfied that it is in the interests of justice that there should be a retrial."
The ruling follows a hearing in March during which allegations were made about the credibility of Waad al-Baghdadi, the key witness in the case against Dizaei.
A jury found Dizaei guilty of attempting to frame Mr Baghdadi when they fell out over money.
During the trial, jurors heard allegations that the Iranian-born officer threatened, assaulted, falsely arrested and faked evidence against Mr Baghdadi, who built him a vanity website.
But Michael Mansfield QC, for Dizaei, had argued that his conviction was unsafe.
Later Dizaei's solicitor Stephen Fox, from Ralli Solicitors, said the former police chief was "relieved" his conviction had been quashed and he could again "call himself an innocent man".
But there was to be a retrial later this year and he was restricted in what he could say today.
Mr Fox said: "He and his family are very pleased that the Court of Appeal quashed this verdict against him."
Hopefully he would be released shortly and reunited with his wife, Shy.
A CPS spokesman said: "The Court of Appeal has ordered that Ali Dizaei should be retried for perverting the course of justice and misconduct in public office.
"The court has said that a jury should have the opportunity to decide whether the prosecution evidence is sufficient to prove the case against Mr Dizaei, considering the new material relating to the alleged victim.
"The Crown Prosecution Service accepts the judgment and will prepare for the retrial.
"It is important that all defendants receive a fair trial, and so it would be inappropriate to comment further at this stage."
Dizaei was convicted by a jury of misconduct in a public office and doing acts with intent to pervert the course of justice.
Lord Justice Hughes said: "He was at the time a very senior serving police officer.
"The allegation was that in the course of a minor and wholly personal dispute with a civilian he arrested the man for threatening behaviour when he knew there was no justification for doing so, thus abusing for personal reasons the considerable power given to him for public purposes."
In his challenge Dizaei relied, said the judge, "on material going to the general credit of the other party to the personal dispute".
One of the allegations was that Mr Baghdadi had committed benefit fraud.
Lord Justice Hughes said fresh information about benefit claims would obviously have had some impact on the jury's deliberations.
The Court of Appeal, "which cannot and should not attempt to make itself into a jury in order to assess the whole case, on paper and without seeing the witnesses, simply do not know whether this conviction is soundly based or not".
He concluded: "In those circumstances we are driven to the conclusion that it cannot be regarded as safe."Reuse content