Heather Mills claims a senior Mirror Group reporter admitted to hacking voicemails left for her by her then boyfriend Sir Paul McCartney.
Mills told BBC's Newsnight that the journalist made the admission in 2001 after she threatened to tell the police.
According to Ms Mills, the Mirror Group journalist rang her some time after McCartney left her a voicemail and "started quoting verbatim the messages from my machine". She claims she then challenged the journalist, saying: "You've obviously hacked my phone and if you do anything with this story … I'll go to the police."
The journalist allegedly responded saying: "OK, OK, yeah we did hear it on your voice messages, I won't run it."
Mills said McCartney had left the voicemail after the couple had rowed. She was in India at the time.
Newsnight confirmed that the senior Mirror Group employee in question was not Piers Morgan, who was editor of the Mirror at the time.
Morgan issued a statement saying: "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."
But the incident described by Mills chimes with an incident that Morgan described in the Daily Mail in 2006, a spokesman for the programme said.
Morgan wrote in the Daily Mail in 2006: "At one stage I was played a tape of a message Paul had left for Heather on her mobile phone. It was heartbreaking."
"The couple had clearly had a tiff, Heather had fled to India, and Paul was pleading with her to come back."
"He sounded lonely, miserable and desperate, and even sang “We Can Work It Out” into the answerphone."
Morgan claims the BBC had verified that the Mirror Group reporter in question was not employed by the Daily Mirror.
Mirror Group Newspapers is part of Trinity Mirror plc, which publishes over 260 titles including the Daily and Sunday Mirror, Daily Record and People.
A Trinity Mirror spokesman said: "Our position is clear. All our journalists work within the criminal law and the PCC code of conduct."
In light of these latest revelations Tory MP Therese Coffey has called for Piers Morgan to return to Britain to aid police with their inquiries into illegal phone hacking.
Phone hacking: News International deleted thousands of emails
