Piers Morgan's bio on Twitter is just one line, a quote from Mad Max Beyond Thunderdome: "One day you're the cock of the walk, the next a feather duster." The first part of that quote is a reference to the old idiom for someone who acts like he's more important than he is, and the second part is, well… it's a pretty good metaphor for the gauntlet through which Morgan's been running since the News Corp. phone hacking scandal flared up in June. The latest accusation from Heather Mills, Paul McCartney's ex-wife, that Piers Morgan listened to a voicemail obtained by hacking her phone has dealt a new round of heavy blows to the already image-battered CNN host.

Thursday morning, deputy leader of the Labour party Harriet Harman told Sky News that Morgan "has got to answer" questions about Mills's accusations and put pressure on Morgan to return to the U.K. for questioning. "Morgan … said he heard a 'heart-breaking' phone message, which clearly gives rise to the assumption that he'd heard a tape-recorded message," said Harman. Morgan has so far denied any illegal behavior during his tenure with British tabloids. (Morgan served as editor of News of the World from 1994 to 1995 when he took the top job at the Daily Mirror, a position he held until 2004.) In a statement released Thursday, Morgan called Mills's claims "unsubstantiated." But MP Harman sounds serious. Following her statement the Labour party later issued a press release repeating Harman's order:

It’s not good enough for Piers Morgan just to say he’s always stayed within the law. There are questions about what happened with Heather Mills’ phone messages that he needs to answer.

Teresa Coffey, a member of Parliament from the rival Tory party and a member of the committee investigating phone hacking, echoed Harman's call for Morgan to return to the U.K. for questioning:

I just hope that the police take the evidence and go with it and if Mr Morgan wants to come back to the UK and help them with their inquiries, and I don't mean being arrested in any way, I'm sure he can add more light.

I don't see any point in him necessarily just staying in the US and issuing statements. I think it would help everybody, including himself and this investigation, if he was able to say more about why he wrote what he did in 2006.

The beckoning from Parliament comes just days after Mark Lewis, lawyer of the victims from the News of the World phone hacking, announced that legal action was being prepared against the Trinity Mirror Group. Meanwhile, MP Tom Watson is reading Morgan's diaries and expects more revelations implicating individuals outside of News Corp.

Before getting into what lies ahead for Mr. Morgan, it's worth unpacking exactly what Heather Mills' accusations mean. Mills told the BBC on Wednesday that a reporter from the Mirror Group--not Piers Morgan--more or less admitted to hacking her phone in 2001. The exchange, of course, comes entirely from Mills' memory. Second, she points out that Piers Morgan bragged about listening to the "heart-breaking" message in a 2006 column for the Daily Mail.

Now, this is where it gets tricky, so bear with me. As soon as the BBC published their report on the interview with Heather Mills, Morgan issued a statement denying that the conversation between Mills and a Daily Mirror Group journalist ever took place: 

Heather Mills has made unsubstantiated claims about a conversation she may or may not have had with a senior executive from a Trinity Mirror newspaper in 2001. The BBC has confirmed to me that this executive was not employed by the Daily Mirror.

I have no knowledge of any conversation any executive from other newspapers at Trinity Mirror may or may not have had with Heather Mills. What I can say and have knowledge of is that Sir Paul McCartney asserted that Heather Mills illegally intercepted his telephones, and leaked confidential material to the media. This is well documented, and was stated in their divorce case…

And to reiterate, I have never hacked a phone, told anyone to hack a phone, nor to my knowledge published any story obtained from the hacking of a phone.

This is vintage Morgan, says Roy Greenslade at The Guardian, who blogged about the McCartney-Mills voicemail last week. Greenslade points out that so far, Morgan admits to listening to the message but "has not specifically addressed" how his paper acquired the McCartney-Mills voicemail. Morgan's latest denial also fails to do that, and in fact, "his admission gives a measure of credence to Mills's allegations," says Greenslade. Furthermore, Greenslade thinks that Morgan's lack of sympathy to the severity of the issue is most condemning:

It's all about the fact that his past remarks on the subject show that he didn't believe it was ethically wrong to engage in the practice. (No other editor, you might note, has left any such hostages to fortune).

In a series of typically show-off statements, he made it clear that (a) hacking was no big deal, (b) he knew how to do it, and (c) lots of journalists were at it.

This latest revelation can be added to a list of other connections between Morgan and shady practices on Fleet Street. Morgan has already picked a fight with a Member of Parliament, publicly thanked Vodafone for their "lack of security" and admitted that he was "quite happy to be parked in the corner of tabloid beast" despite all of the questionable practices that his reporters were supposedly doing.

Is Heather Mills accusation the smoking gun connecting Morgan to the phone hacking scandal that so many people have been looking for? That depends on whether or not it's true. Regardless, it's another damaging blow to Morgan in a desperately important PR battle. Since being directly implicated in the scandal in mid-July, the ratings for Morgan's CNN chat show have dropped significantly. Even though Morgan has been careful with his words, it seems likely that Parliament is unsatisfied, and he'll be called in to answer questions. And based on recent statements, politicians of both parties seem quite prepared to put Morgan in his place.

Update: The BBC reports: "MPs on the culture select committee say they have no plans to call ex-Mirror editor Piers Morgan or Mirror Group executives to face questions over Heather Mills' phone-hacking claims."