The former Scotland Yard commissioner who quit over the phone-hacking scandal will give evidence to the Leveson Inquiry into press standards today.
Sir Paul Stephenson resigned last July after coming under fire for hiring former News of the World executive editor Neil Wallis as a PR consultant and for accepting free accommodation at a luxury health spa worth thousands of pounds.
The inquiry will also hear from Elizabeth Filkin, author of a recent report into relations between the Metropolitan Police and the media that advised officers to avoid "flirting" and accepting alcohol from journalists.
Roger Baker, from Her Majesty's Inspectorate of Constabulary, will give evidence about his 2011 review of police relationships which found corruption was not endemic but that there was a "hugely inconsistent approach" across forces in their attitude towards free gifts.
Scotland Yard's original phone hacking inquiry resulted in the jailing of News of the World royal editor Clive Goodman and private investigator Glenn Mulcaire in January 2007 after they admitted intercepting voicemail messages left on royal aides' phones.
However, the Met was widely criticised for limiting the scope of the investigation, despite evidence from Mulcaire's notebooks that there could be many more hacking victims.
Last week Scotland Yard's former head of counter-terrorism, John Yates, told the Leveson Inquiry he was "good friends" with Mr Wallis and "may well" have drunk champagne with the News of the World's crime editor.
But he insisted his links with the paper did not affect his decision not to reopen the phone-hacking inquiry after The Guardian published a story in July 2009, revealing the illegal practice was far more widespread than previously believed.
"I absolutely know and I guarantee that none of that played any part in my decision making. My conscience is completely clear on that," he said.
The inquiry will hear from former Met commissioners Lord Condon and Lord Stevens tomorrow, and from former commissioner Lord Blair on Wednesday.
Prime Minister David Cameron set up the Leveson Inquiry last July in response to disclosures that the News of the World hacked murdered schoolgirl Milly Dowler's phone after she disappeared in 2002.
The first part of the inquiry, sitting at the Royal Courts of Justice in London, is looking at the culture, practices and ethics of the press in general and is due to produce a report by September.
The second part, examining the extent of unlawful activities by journalists, will not begin until detectives have completed their investigation into alleged phone hacking and corrupt payments to police, and any prosecutions have been concluded.