The officer in charge of the original phone hacking inquiry has been called to give further evidence to MPs.
Former Assistant Commissioner Andy Hayman will be questioned over “who knew what at which point”, Keith Vaz, chairman of the Commons Home Affairs Select Committee said.
Mr Hayman, who was in charge of the 2006 investigation, will give evidence on Tuesday with Deputy Assistant Commissioner Sue Akers, who is in charge of the current probe, Operation Weeting.
Former Assistant Commissioner Peter Clarke, of Scotland Yard’s specialist operations division, will also be questioned by MPs on the committee.
Mr Vaz said: “These allegations are extremely shocking.
“It is now essential that any parties involved criminally are prosecuted and that we uncover who knew what at which point in time at both the Metropolitan Police and at the News of the World.
“The Committee will be raising this issue with police officers involved in the current and previous investigations.
“We will also seek to clarify why a significant variance of action was taken by mobile phone companies in the aftermath of the phone hacking revelations.”
Mr Vaz has also written to Acting Commissioner John Yates and News International chief executive Rebekah Brooks, asking what prior knowledge there had been of hacking in the Milly Dowler case.