London: A top British undercover reporter known as the “Fake Shaikh” for his elaborate disguises when meeting celebrities went on trial, on Wednesday, accused of doctoring evidence in a pop star’s drug case.

Mazher Mahmood, 53, was known for his scoops for The Sun on Sunday newspaper, in which he would pose as a wealthy figure from the Middle East and encourage celebrities into making embarrassing revelations.

He and his driver, Alan Smith, deny conspiracy to pervert the course of justice over the 2014 trial of Tulisa Contostavlos, a former member of hip-hop group N-Dubz and X Factor talent show judge.

Contostavlos was accused of arranging for Mahmood to be supplied with half an ounce of cocaine, a story which landed him an exclusive for The Sun on Sunday and, when he handed evidence to police, led to her prosecution.

Prosecutors claim Mahmood, who dubbed himself “King of the Sting”, and Smith altered a police statement from Smith to remove negative comments by Contostavlos about cocaine which could have helped her lawyers.

“Mazher Mahmood had a vested interest in the prosecution succeeding in terms of his reputation and his standing,” lead prosecutor Sarah Forshaw told the Old Bailey central criminal court in London.

“In effect, the hearing in June 2014 put Mr Mahmood and his journalistic process on trial,” she added.

“He knew that if it could be shown that he had acted improperly as an agent provocateur, inducing Miss Contostavlos to do something she would not otherwise do, his own credibility and standing and the prospect of conviction in the case might both be severely damaged.”

In his “Fake Shaikh” guise, Mahmood posed as a film producer when he met Contostavlos in 2013, knowing she wanted to break into the movies, and told her she could be cast alongside Leonardo di Caprio, Forshaw said.

After meeting at a five-star hotel in London’s exclusive Mayfair district, Smith drove Contostavlos and some companions home.

He overheard a conversation in which, “Tulisa had spoken about someone in her family being dependent on cocaine” and was “negative” about the drug, she added.

At the original trial, which collapsed, the pop star was alleged to have arranged to supply Mahmood with cocaine after that.

At first, Smith recounted the car conversation as part of his evidence to police but the day after, he allegedly contacted officers saying they should remove the anti-drugs part.

“A second statement was prepared and it was how that change of account came about that lies at the heart of this case,” Forshaw said.

In the intervening 24 hours, Mahmood and Smith allegedly exchanged a string of texts and calls.

But texts and emails between them had been destroyed by the time police accessed their phones, the prosecutor added.

Mahmood, of Purley in south London, and Smith, from Dereham in Norfolk, eastern England, watched silently from the dock as the case against them was outlined.

Their lawyers will outline the defence case later in the trial.