The original Met phone hacking investigation, launched in December 2005, failed to identify hundreds of victims.
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.
But no action was taken against any other reporters and the inquiry failed to identify hundreds of victims.
One source close to the U.S. investigation told the Independent on Sunday: 'The FBI made it perfectly clear that if the British police drop the ball on this they will pick it up and run with it.'
As well as evidence from News Corp, the FBI is also gathering evidence from the Leveson Inquiry and other parliamentary select committees.
It is thought that the Murdoch empire fears a U.S. investigation due to the potential for longer jail terms and more severe financial penalties, the newspaper said.
This is believed to be why it has increased its efforts to help police over the past few months - including handing over thousands of potentially incriminating emails.
The FBI has reportedly found no evidence of phone hacking within News Corp in the U.S., Murdoch's holding company based in New York.
Earlier this week Rebekah Brooks and her racehorse trainer husband Charlie were arrested in dawn raids by police investigating allegations of a cover-up in the phone hacking inquiry.
The former News International chief executive and her husband were held on suspicion of conspiracy to pervert the course of justice.
They were among six people detained by detectives from Operation Weeting, the inquiry into illegal hacking of voicemail messages.
Mrs Brooks, the former editor of The Sun and the News of the World, has been on bail since last summer when she was arrested on suspicion of phone-hacking and corruption.
That arrest in July was ‘by appointment’ but yesterday the couple were woken by a sharp, unexpected, knock on the front door of their Cotswolds mansion.
The number of people arrested in Operation Weeting, which has been running since last January when police reopened investigations, stands at 21.
Two other linked investigations – Operation Elveden into corrupt payments to police and Operation Tuleta into computer hacking – have resulted in 26 arrests.