The witness whose evidence convicted former Scotland Yard commander Ali Dizaei is a fraudster, an appeal court judge has said.

Dizaei is appealing against his conviction for assaulting Waad al-Baghdadi, 25, in a row over money outside a London restaurant, and then trying to frame him. Lawyers for Dizaei told the court of appeal the conviction last year was no longer safe because Baghdadi had lied to secure thousands of pounds of benefits, as well as in his court evidence.

The court heard Baghdadi lied to the pension and benefits officials to pretend his father was alive and collect his £100 a week pension, plus an allowance for caring for him long after he had died. Thousands of pounds in benefits went into bank accounts controlled by Baghdadi, said Michael Mansfield QC, representing Dizaei. The fraud went on after his father's death in 2006 until six weeks ago, in February this year. Baghdadi was arrested over the fraud on 6 March, and bailed until May.

In all Baghdadi claimed £18,000 from an attendance allowance for his dead father, a carer's allowance, and a pension as well as income support. There was also an application to the social fund for a loan bearing the signature of his dead father, the court heard.

Mansfield also alleged Baghdadi had lied to get into Britain, claiming he was fleeing persecution from Iraq when he had been born and raised in Iran, and this falsehood had been repeated by Baghdadi at the trial of Dizaei, where his accuser had also wrongly stated his real name, age, as well as his nationality.

Some of the fraud, said Mansfield, was continuing at the time of the 2008 clash with Dizaei and at the time of the trial where Baghdadi was presented as a witness of truth.

Mansfield said the evidence showed He was capable of a "pattern of persistent and elaborate deceit" and in recent police interviews was still not telling the truth.

Lord Justice Hughes said he accepted there was the "clear prima facie case he is a fraudster", but told Mansfield he had to show how this made unsafe the jury's decision to believe his evidence over Dizaei's: "It's all very well showing this man is a fraudster, how does it effect the conviction?" Mansfield replied that Baghdadi had been "pivotal" to the conviction.

The crown will argue that much of the material about Baghdadi's benefit claims may have been known by Dizaei at the time of the trial and thus not count as new evidence, needed to overturn the verdict in the original trial.

Peter Wright QC also said that, if the jury been told the evidence about Baghdadi's benefits claims, the crown would have applied to have the jury hear claims that Dizaei was not of good character. Wright said that evidence would have been produced of threatening messages Dizaei had left on the answerphone of a one time lover, which the crown would claim showed he had previously used his position to threaten someone during a row, and also his volatile temper.

Dizaei was an outspoken critic of the police on race, a former leader of the National Black Police Association, and a figure in a racism row that erupted at the top of Scotland Yard in summer 2008.

Dizaei's 25-year police career ended after his conviction and jailing for four years, with him being drummed out of the Metropolitan police in disgrace.

Dizaei was convicted of falsely arresting Baghdadi in a dispute over money and then lying in official statements, claiming he had been assaulted and threatened by Baghdadi.

The crown alleged that on 18 July 2008, Dizaei clashed with 24-year-old Baghdadi, who claimed the police commander owed him £600 for a website he had designed.

The hearing continues.