The number of UK police officers investigating phone hacking has increased from 45 to 60, BBC quoted the Scotland Yard as saying.
The move came following a significant increase in the workload over the past fortnight, Metropolitan Police Deputy Assistant Commissioner Sue Akers said.
She said there had been a "surge of inquiries and requests for assistance from the public and solicitors".
A few hours before Cameron faced legislators, a cross-party parliamentary committee published a report criticising both News International, the British arm of News Corp, and the police over the phone-hacking investigation.
"There has been a catalogue of failures by the Metropolitan Police, and deliberate attempts by News International to thwart the various investigations," said Keith Vaz, the chair of the Home Affairs committee.
On Monday two top police officers, Metropolitan Police Commissioner Paul Stephenson and Assistant Commissioner (AC) John Yates, resigned under the mounting pressure over the handling of the phone hacking scandal.