Andy Coulson is under mounting pressure over phone hacking allegations at the News of the World (Source: PA)

Pressure continues to mount on the prime ministerial strategist and former News of the World editor Andy Coulson, with MPs announcing that they will be launching a new inquiry into allegations of illegal phone hacking at the publication.

The announcement of the new inquiry came shortly after MPs were told that Coulson, who edited the News of the World between 2003 and 2007, would be questioned by police over the hacking allegations. Coulson, who is now David Cameron's director of communications, has repeatedly pleaded ignorance, denying that he condoned or had knowledge of phone hacking during his time as editor.

Keith Vaz, the chairman of the home affairs select committee, said yesterday afternoon that concerns expressed by the Metropolitan police justified a new investigation.

"The evidence of Assistant Commissioner John Yates raised a number questions of importance about the law on phone hacking, the way the police deal with such breaches of the law and the manner in which victims are informed of those breaches," Vaz said.

"I hope this inquiry will clarify all these important areas."

According to BBC News, it is not the intention of the MPs to call witnesses to public hearings; rather, the inquiry shall be conducted by writing.

The re-emergence of the scandal - which threatens to engulf the prime minister's office, the News of the World and some of its most senior employees - has already brought one potential star witness out of the woodwork. Ross Hall, the man who reportedly transcribed hacked messages, told The Guardian that he was willing to speak to both the MPs' inquiry and the Metropolitan Police.

Asleep at the wheel?

Assistant Commissioner John Yates, appearing before home affairs committee (Source: PA)

The latest developments were triggered by a detailed expose in The New York Times last week, which suggested that Coulson has repeatedly lied about his role in phone hacking. According to one reporter who worked with him, not only did Coulson have direct knowledge of phone hacking at the publication - contrary to his public denials - but that he condoned the practice and "actively encouraged" others to continue the practice of intercepting phone messages.

John Yates told MPs that The New York Times had rejected Met requests for assistance regarding the phone hacking allegations due to journalistic privilege, adding that he was "not hopeful" that the American publication would budge.

The emergence of new allegations has raised questions about how phone hacking was previously dealt with by Scotland Yard and the Home Office. Earlier this week, a leaked memo came to light which showed that the Home Office had decided against beginning an independent inquiry into phone hacking, because it thought that the Met would "deeply resent" the action and would interpret it as a vote of no-confidence in Scotland Yard's capabilities.

Scotland Yard's inquiry in 2006 led to the jailing of Clive Goodman, the paper's royal reporter, and Glenn Mulcaire, a private investigator who worked for Goodman on phone hacking. But claims have persisted since then that hacking was far more widespread, and that police had made an error of judgement by focusing on Goodman and Mulcaire.

Yates conceded in his appearance before the home affairs committee that it may have been a mistake not to interview Neville Thurlbeck, the News of the World's chief reporter, during the course of the Met's inquiry. Evidence presented by The Guardian's Nick Davies before MPs last year included an email with 35 hacked phone messages attached, and described as "the transcript for Neville".

Media Spy discussion: International Journalism and Media