Twenty-five convictions secured through evidence given by British reporter Mazher Mahmood, nicknamed the Fake Sheikh, will be reviewed due to doubts over his reliability as a witness, prosecutors said Thursday.

Infamous for often reporting undercover posing as a wealthy Arab dressed in robes and a keffiyeh, his evidence has helped secure convictions in several high-profile cases including on drug charges involving celebrities and sporting figures.

His methods, though, have been criticized and several of his targets have complained of entrapment.

In July, a case against pop star Tulisa Contostavlos, who was accused of offering to procure cocaine for Mahmood, collapsed after the judge said he had "strong grounds to believe" Mahmood had lied at a hearing before the trial started.

A Crown Prosecution Service spokesman said this had prompted the body to look again at convictions secured through evidence supplied by Mahmood.

"We are now considering past cases which resulted in a conviction in criminal courts in England and Wales based on evidence provided by Mr Mahmood, and have identified 25 cases," the CPS said in a statement.