What is Operation Rubicon?

Operation Rubicon detectives have been looking at whether certain witnesses lied to the court during Sheridan's trial as part of a "full" investigation into phone hacking in Scotland.

Mr Coulson, then employed by Downing Street as director of communications, told the trial in December 2010 he had no knowledge of illegal activities by reporters while he was editor of the News of the World.

He also claimed: "I don't accept there was a culture of phone hacking at the News of the World."