The FBI has vowed to step in if the Met Police 'drop the ball' in its investigation into illegal activity within the Murdoch empire, it has been revealed.

The U.S. Bureau already has access to all the evidence handed over by News Corporation to Scotland Yard and the company apparently has a legal team of 'big guns' ready to handle inquiries from detectives.

The original Met phone hacking investigation, launched in December 2005, resulted in the News of the World’s royal editor Clive Goodman and private investigator Glenn Mulcaire being jailed for intercepting voicemail messages.