The singer leaves Southwark Crown Court in London as the case against her has been suddenly dismissedReuters

The drugs trial of N-Dubz star Tulisa Contostavlos has been thrown out of court after a judge said that there were "strong grounds" to believe an undercover Sun reporter has lied under oath.

In a dramatic turn of events, the jury heard that Mazher Mahmood, who posed as a fake sheikh as part of a drugs sting, had been untruthful at a hearing ahead of the trial.

Dismissing the case, Judge Alistair McCreath told Southwark Crown Court that it "cannot go any further".

Contostavlos was accused of acting as a fixer by introducing him to her friend Mike GLC who supplied the £860 worth of cocaine at London's Dorchester Hotel in May 2013.

Mahmood is said to have also offered the 26-year-old star a leading role in a Slumdog Millionaire-type film tipped for Oscar glory.

Throughout the trial, the singer denied brokering the deal that saw Mahmood obtain 0.5oz (13.9g) of the Class A drug.

The former X Factor judge's co-defendant, Mike GLC, whose real name is Michael Coombs, previously pleaded guilty to supplying cocaine. He is now expected to walk free after the judge said the case could not proceed against him.