Fake Sheikh's editor fails to find evidence for his grand claim to Leveson

Former News of the World reporter faces fight to save name after claiming he nailed 261 criminals

Britain's most mysterious investigative journalist, Mazher "The Fake Sheikh" Mahmood, has made an admission that suggests his claim to have brought 261 criminals to book might be as dubious as his famous dishdasha disguise.

The former News of the World investigations editor, who has donned Arab robes to dupe a succession of high profile victims ranging from the Countess of Wessex to former England manager Sven Goran Eriksson, is being accused of perjury over his assertion to the Leveson Inquiry that his journalism had led to in excess of 250 criminal prosecutions.

In a fresh statement to Leveson, Mahmood – who now works for The Sunday Times – has acknowledged that an investigation conducted by the law firm Linklaters for his employer News International at the behest of The Sunday Times editor John Witherow, has found evidence of 94 individual convictions.

Since his appearance at the inquiry last December, Mahmood's reputation has come under intense scrutiny with a Channel 4 documentary earlier this month focusing on his methods. Jockey Kieren Fallon, who won damages and an apology from the News of the World following a Mahmood investigation, told the programme: "They destroy people's lives. I was suicidal about it and you can't put a price on that."

A separate investigation into Mahmood's claims was made by television journalist Paddy French of Rebecca Television who studied News of the World archives and found evidence of 70 successful criminal prosecutions. As a result, Mr Witherow ordered a "thorough investigation" into Mahmood's figure.

Mr Mahmood has already been criticised by Lord Justice Leveson over his evidence on the circumstances surrounding his departure from The Sunday Times in 1988.

The reporter told the inquiry he had left following a "disagreement" with his senior colleagues, when in fact he had been dismissed for tampering with a computer in order to cover up a mistake.

After Rupert Murdoch closed the News of the World in July 2011 as a result of the phone-hacking scandal, Mahmood's work took pride of place in the paper's defiant final edition to show how the tabloid could be a force for public good.

The Sunday Times will not be enjoying the latest scrutiny. News International has gone to great lengths to protect its quality titles from the fallout from the phone-hacking affair and a parallel police investigation into the alleged bribery of public officials which has led to a series of arrests at The Sun.

In his latest statement, Mahmood admits keeping only a "broad running check" on the number of prosecutions he was responsible for and had "not kept records and clippings of each and every case". He said he had included 140 illegal immigrants in his total but was told by Linklaters that "it is unlikely these individuals would have been the subject of criminal prosecutions".

Mahmood disputes the Linklaters total. "I am confident that my work as a journalist has led to substantially more convictions than the 94 which Linklaters has been able to verify," he told the judge.