Senior Metropolitan Police officers will be quizzed by MPs in public later about inquiries into phone hacking at the News of the World.
MPs are expected to ask two former officers why the initial investigation in 2005 failed to uncover evidence of hacking of crime victims' phones.
Asst Commissioner John Yates, who ruled out reopening the inquiry in 2009, will also face the home affairs committee.
Keith Vaz MP, chair of the committee, said the main priority was to work out a timeline of the investigation, and to understand why "information that was given was perhaps different to what they intended to give".
Former Mayor of London Ken Livingstone said that there has been "far too close a relationship" between the media generally and police officers conducting active investigations.
He said it was a "completely spurious" argument that at any point in the inquiry police did not have the resources to look thoroughly into the hacking allegations.
"This is a scandal that goes right to the heart of the establishment," he said, calling for an "arms length" relationship between the media and politicians.
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