Tulisa Contostavlos' trial on drug charges has collapsed after a witness for the prosecution had their evidence called into question.

The jury at Southwark Crown Court heard that the trial had collapsed as Judge Alistair McCreath believes that undercover reporter Mazher Mahood "told lies".

The judge said: "There are strong grounds for believing that Mr Mahmood told me lies when he gave evidence," and added that as a result the case now "cannot go any further".

The jury has now been formally discharged.

Former X Factor judge Contostavlos read a statement on the steps of the court, saying: "I have not been able to work for a year and I'm now looking forward to resuming my career. I will use these experiences to make me stronger. 

"I would like to thank all the people who have supported me through this terrible ordeal, including my fans and, of course, my legal team."

Contostavlos had pleaded not guilty to a charge of being concerned with the supply of class A drugs.

The story was was reported in The Sun on Sunday newspaper in June 2013.

A spokesperson for the publication said that Mahood has been suspended pending an internal inquiry.

They said: "We are very disappointed with this outcome, but do believe the original investigation was conducted within the bounds of the law and the industry's code. This was demonstrated by the CPS decision to prosecute.

"The Sun, of course, takes the judge's remarks very seriously.

"Mr Mahmood has been suspended pending an immediate internal investigation."