Piers Morgan is facing calls to return to Britain to answer questions about phone hacking as the controversy over how much he knew about the practice showed no signs of abating.

John Whittingdale, the Conservative MP who chairs the Commons culture, media and sport committee, said it was right that the former Daily Mirror editor should return from the US, where he hosts a CNN chatshow.

Whittingdale said: "Therese Coffey [a Tory member of the committee] said he should come back to this countryto answer questions and I think that is absolutely right. He certainly should."

Harriet Harman, Labour's deputy leader, said Morgan had questions to answer, citing a column he wrote five years ago in which he wrote that he had once been played a message left on a mobile phone belonging to Heather Mills.

Harman said: "Hacking is a criminal offence and … every allegation has got to be thoroughly investigated by the police. We started off with just the News of the World … it's clearly been much more widespread than people have been prepared to admit."

Morgan, who edited the Daily Mirror for nearly 10 years until 2004, said in a Daily Mail column in 2006 that he had heard the message, which was left by Sir Paul McCartney on Mills's phone after the couple had an argument. He said the former Beatle sounded "lonely, miserable and desperate".

Paul McCartney said he intended to step into the phone hacking controversy and contact British police because, he said, "apparently I have been hacked".

Speaking from Ohio, where he is on tour, the former Beatle told journalists in Los Angeles that once back in Britain he would be talking to detectives about the alleged incident, which appears to be a reference to the claims raised by his former wife Heather Mills.

Though he gave no details, including which newspaper had allegedly carried out the hacking, he said: "I do think it's a horrendous violation of privacy. I do think it has been going on for a long time and I do think more people than we know knew about it."

Mills told the BBC's Newsnight this week that a senior journalist on a paper owned by Trinity Mirror, the Daily Mirror's parent company, conceded to her in 2001 that he had obtained information about an apology left by McCartney by listening to her phone messages.

According to Mills, the journalist rang her and "started quoting verbatim the messages from my machine".

She said she challenged him, saying: "You've obviously hacked my phone and if you do anything with this story … I'll go to the police."

Mills said he responded: "OK, OK, yeah, we did hear it on your voice messages, I won't run it."

Morgan has consistently denied he has ever hacked a phone, ordered any of his journalists to do so, or published any story obtained from the hacking of a phone.

He issued a statement through CNN, for whom he records Tonight with Piers Morgan, in response to Mills's claims pointing out that a high-court judge had described her as an unreliable witness.

"No doubt everyone will take this and other instances of somewhat extravagant claims by Ms Mills into account in assessing what credibility and platform her assertions are given," he said.

Morgan used Twitter to ridicule the prominence of the story on Thursday, posting: "Morning all, lovely day in LA. Anything going on back home in UK? Seems a bit quiet over there … so heart-warming that everyone in UK's missing me so much they want me to come home."

Trinity Mirror, which also owns the Sunday Mirror and the People, said on Thursday: "All our journalists work within the criminal law and the PCC code of conduct and we have seen no evidence to suggest otherwise."

The publisher of the Daily Mail said it too is reviewing its editorial controls. Associated Newspapers said its head of editorial legal services, Liz Hartley, would be carrying out the review.

The company publishes the Daily Mail, Mail on Sunday and the Metro. In a statement, Associated Newspapers said: "Liz Hartley, head of editorial legal services, who has responsibility for overseeing compliance with the company's policy on journalistic standards, has asked Eddie Young … to join her to assist in a review of our editorial controls and procedures."

Last month Daily Mail editor Paul Dacre said he had never "countenanced" hacking or blagging on his newspaper.

Meanwhile the FBI is widening its investigation of News Corporation's activities within the US to look at whether allegations of computer hacking by one of its subsidiaries was an isolated case or part of a "larger pattern of behaviour", Time magazine is reporting.

Time suggests that the FBI inquiry has been extended from a relatively narrow look at alleged malpractices by News Corp in America into a more general inquiry into whether the company used possibly illegal strongarm tactics to browbeat rival firms, following allegations of computer hacking made by retail advertising company Floorgraphics.

In a civil lawsuit against News Corp in 2004 Floorgraphics told a court that its website had been breached 11 times over four months without authorisation. The source of the alleged hacking was traced back to an IP address registered to News America in Connecticut. Morgan edited the Daily Mirror for nearly ten years before he was sacked in 2004 from the Daily Mirror for publishing photos of British soldiers abusing Iraqi prisoners which turned out to be false.