Despite Mr Morgan's denials of any sanctioning of phone hacking, and his insistence that Heather Mills, the former wife of Sir Paul McCartney, is an unreliable witness to the alleged hacking of her phone messages, MPs piled the pressure on for him to return to Britain to reveal what he knew about an alleged interception in 2001.
The Labour deputy leader, Harriet Harman, said the police should now look into claims made by Ms Mills that the newspaper group listened to messages left for her by the former Beatle. "It's not good enough for Piers Morgan just to say he's always stayed within the law," Ms Harman said. "There are questions about what happened with Heather Mills's phone messages that he needs to answer."
John Whittingdale, chairman of the Culture, Media and Sport Select Committee, which is investigating phone hacking, said that while it was powerless to summon him to give evidence before MPs, the CNN host had "serious questions" still outstanding.
"I hope he will return to the UK and I imagine that there will be some questions which will be put to him, possibly by the police, on the basis of the evidence that has emerged," he said.
Sir Paul broke his silence over the scandal yesterday to say that he planned to contact police about allegations that his voicemail messages may have been intercepted. "I will be talking to them about that," he said, speaking via video-link from Cincinnati, Ohio to US journalists. "I don't think it's great," he said. "I do think it is a horrendous violation of privacy, and I do think it's been going on a long time, and I do think more people than we know knew about it. But I think I should just listen and hear what the facts are before I comment."
At the heart of the allegations is Mr Morgan's bitter relationship with Ms Mills. It is easy to portray the recent claims against him as the settling of old scores from a woman he has repeatedly criticised as a "ludicrous, hypocritical, shameless, grasping creature".
It was Mr Morgan (who was editor of the Daily Mirror from 1995 to 2004) who introduced Ms Mills to Sir Paul at the inaugural Mirror Pride of Britain Awards. Ms Mills was a regular judge on the newspaper's high-profile awards panel.
But two years later, the first signs of strain were creeping into the McCartney-Mills relationship. She was in India and the two had quarrelled. McCartney, in an attempt to woo back his new-found love, left a series of voicemails on the former model's phone.
According to a senior Mirror Group journalist, these messages included Sir Paul serenading his girlfriend by singing "We Can Work It Out". Ms Mills claims the contents of the messages were quoted back to her "verbatim" by the reporter, who – it is alleged – acknowledged they had been illicitly listened to.
Mr Morgan has fiercely denied any involvement in phone hacking despite a 2006 Daily Mail article in which he described listening to a recording of a "heartbreaking" voicemail message left by the former Beatle. Trinity Mirror also denies any wrongdoing.
In his statement, however, Mr Morgan dismissed Ms Mills's claims that she was hacked as "extraordinary" and "unsubstantiated", and alludes to allegations that surfaced during her divorce case from Sir Paul in which her evidence was described by the judge as "less than candid".
In a statement yesterday, Ms Mills said she "looks forward to receiving Piers Morgan's answer as to how he knew the content of her private voicemail messages".
Career landmarks: Piers Morgan vs Heather Mills
Piers Morgan and Heather Mills have been dogged by controversy throughout their careers. Rarely has there been a dull moment:
Piers Morgan
1996 Criticised for publishing "Achtung! Surrender" headline the day before England's Euro 96 clash with Germany in Daily Mirror
2000 Investigation into claims of illegal share ramping begin. Morgan is cleared of wrongdoing in 2004
2004 Forced to resign after publishing fake photographs of British troops abusing Iraqis
2006 Admits to hearing a voicemail message left by Paul McCartney on Heather Mills' phone
Heather Mills
1993 Ms Mills is hit by a motorbike, losing part of her leg in the accident.
1999 Meets Sir Paul McCartney at Mirror Pride of Britain Awards.
2002 The couple marry in ceremony in Ireland; they have a child a year later.
2008 Mills is awarded £24.3m divorce settlement – but the judge criticises the reliability of her evidence.
2006 Accused by journalist, also called Heather Mills, of impersonating her throughout the 1990s to land television jobs.
2007 Complains in an interview that she has received "worse press than a paedophile or a murderer".
2008 Awarded a £24.3m divorce settlement – but the judge criticises her evidence, calling it "inconsistent and inaccurate".
2011 Claims that a journalist working for the Mirror Group admitted to hacking her phone.
