The case against a "Fake Sheikh" alleged to have tampered with evidence in the collapsed drugs trial of Tulisa Contostavlos is "fundamentally flawed," a court has heard.

Mazher Mahmood, 53, of Purley, and his driver, Alan Smith, 67, are on trial at the Old Bailey accused of plotting to pervert the course of justice.

The pair allegedly suppressed anti-drugs comments the former X Factor judge made while travelling home from meeting the undercover Sun journalist at the Metropolitan Hotel in London in May 2013.

Mr Smith's recollection of her conversation about a family member's drug problem would have been useful to the defence but was deleted from the final version of his police statement of June 2014, the Old Bailey has heard.

The former N-Dubz singer's trial for allegedly arranging for Mr Mahmood to be sold £800 of cocaine by one of her contacts was thrown out of court the following month.

In his closing speech, his lawyer John Kelsey-Fry QC told jurors the prosecution's case did not offer a "compelling" argument for his guilt and instead "defies common sense".

"The prosecution approach is fundamentally flawed and illogical and defies common sense," he said.

"These are clearly bold words and I'm going to have to make them stick."

The barrister pointed out that Miss Contostavlos was not being tape-recorded while she was being driven home to Hertfordshire by Smith following the sting.

Afterwards, Smith made no mention of her negative comments about drugs to Mr Mahmood, only that there was rowing in the car, he said.

He added: "If Mr Smith did not tell Mr Mahmood about the drugs conversation at the time, it cannot have seemed significant - not something he was making a mental note of at the time."

When he was giving his statement to police more than a year later, Mr Smith had spoken about it "openly and candidly," the jury was told.

Mr Kelsey-Fry said: "That speaks volumes about MrMahmood and Mr Smith and speaks volumes about the logic of the case."

He went on to say that Mr Mahmood had done "absolutely the right thing" when he advised his long-time associate what to do about his concerns over the accuracy of his initial statement.

He told the jury: "You will note that Mr Mahmood repeatedly insists he did not discuss Smith's evidence with him and he repeatedly insists he could not discuss Smith's evidence.

"While Mr Smith discussed his area of concern, MrMahmood made clear he could not discuss the evidence of the case.

"You know now that if that is what Mr Mahmood told Mr Smith he would be absolutely right, as the prosecution made clear. Witnesses should not discuss their evidence amongst themselves.

"Likewise, if Mr Smith is concerned about the accuracy of the statement, advising Mr Smith to contact the police would be absolutely the right thing to do.

"What Mr Mahmood has said both on oath in court and in his prepared statement as to what he said to Mr Smith would be absolutely the right thing to do."

Mr Kelsey-Fry told jurors the fact that they now know that Miss Contostavlos did have a family member with a drugs problem had "no bearing whatsoever" on what Mr Smith could accurately recall in June 2014.

Mr Kelsey-Fry rejected the prosecution's case that the singer's anti-drugs stance in the car would have stopped her trial "in its tracks".

He told jurors it "cannot begin to undermine the clear and incontrovertible evidence - and Mr Mahmood would know it".

He said Mr Mahmood's whole investigation was about exposing the pop star's private face "smoking weed" and "arranging cocaine for mates" set against her public persona as a "role model".

He added: "Mr Mahmood is not a policeman. He is a journalist.

"Whilst the prosecution may say he boasts of the number of convictions resulting from his work, securing convictions is not actually his job."

Mr Mahmood and Mr Smith, of Dereham, Norfolk, each deny wrongdoing.

The trial continues.