The former Director of Public Prosecutions (DPP) Lord Macdonald was warned by his own employees as far back as 2006 that there were a "vast array" of News of the World phone-hacking victims.
Lord Macdonald, who has since been hired by the newspaper's owner, Rupert Murdoch, was sent a memo nearly six months before the reporter Clive Goodman and the private investigator Glenn Mulcaire were convicted, revealing that the charges they were facing related to just a fraction of the potential victims.
However, the hacking investigation was never widened despite pressure on the police and Lord Macdonald, the head of the Crown Prosecution Service at the time, to do so.
In a letter released yesterday, the former Attorney General Lord Goldsmith revealed: "The Director [of Public Prosecutions] and I were aware that the particular cases referred to were not isolated examples."
Lord Goldsmith said protocol prevented him from speaking to the police, but this did not apply to the Crown Prosecution Service, which Lord Macdonald led at the time, and whose lawyers briefed him on other victims of hacking.
The Met had to reopen its inquiries into criminality by the NOTW in January this year when it became apparent that police and prosecutors had failed to fully investigate the widespread phone hacking by the newspaper five years ago.
The revelation is embarrassing for Lord Macdonald because when he examined emails held by News Corp as part of his new job assisting the company's internal investigation earlier this year, he took "three to five minutes" to decide that the material constituted evidence of criminality and needed to be passed to police.
He told the Home Affairs Select Committee last week: "The material I saw was so blindingly obvious that trying to argue that it should not be given to the police would have been a hard task."
Meanwhile, the Chancellor, George Osborne, who advised David Cameron to hire Andy Coulson as his spin doctor after he resigned as the NOTW's editor over the scandal, said yesterday that he regretted the appointment.