In a dramatic turn to the scandal, former journalists at the Mirror group said they witnessed phone hacking at their newspapers and that the practice was "endemic".
So far, the allegations had clouded newspapers of the News International group, the largely affected being the now closed News of the World.
In fresh developments, James Hipwell, a former journalist of the Daily Mirror told The Independent that he would be willing to testify in front of a public inquiry into the episode headed by Justice Brian Leveson.
The BBC also quoted a former employee of the Sunday Mirror as claiming that he witnessed routine phone hacking in the newsroom, with celebrities including actress Liz Hurley and footballer Rio Ferdinand targeted.
The two newspapers were among the main competitors of News International's tabloids.
However, Trinity Mirror defended itself against the allegations and said its journalists work within the criminal law and Press Complaints Commission code of conduct.
Hipwell, 45, also alleged that hacking took place on other newspapers within the Trinity Mirror group, including The People, where Sean Hoare, the whistleblower who died recently, was working before moving to the News of the World.
"It was endemic. Sean didn't suddenly move from one tabloid where it didn't happen to another where it did. But at the time it wasn't illegal," he was quoted as saying by The Independent.
Hipwell was fired from the Mirror in 2000 over a scandal in which he was accused of buying shares before tipping them in the paper. He was convicted of market manipulation and served 59 days in jail.
The BBC quoted a source as saying that designated reporters at the Sunday Mirror hacked into phones of celebrities pretty much every day.
"One reporter who was very good at it was called the 'master of the dark arts'," he said.
The person also claimed the Sunday Mirror hired a voiceover artist to imitate famous people in order to get information about them.
"He was such a god of a voiceover artist that he could pretend to be famous people or failing that he'd pretend to be their lawyer or someone related to them.
Meanwhile, as investigations continue at various levels in the phone-hacking scandal, survivors of the 2005 London bombings fear that their contact details with the police may have been sold to News of the World journalists.
According to Beverli Rhodes, Chair of the Survivors' Coalition Foundation, many victims suspected that personal contact details, including mobile phone and ex-directory landline numbers as well as home addresses, were passed by police officers to the journalists of the now-defunct News of the World.
She said she had been contacted by survivors of the bombings, who said they had been approached by News of the World reporters with bogus stories of how they obtained their details, which they believe may have originated with the police, The Observer reported today.
Rhodes told the paper that Scotland Yard "had the full list of survivor contact details."
"I am pretty sure that is how the News of the World got my home address. I had only moved there maybe three or four weeks before News of the World reporters turned up. The only place where my new details were stored were the post office, bank, doctor and Scotland Yard," she said.
She said the suspicion is that "the full list was given or sold on to the newspaper or News International or fell into someone's lap when visiting the Yard".
"One of the survivors' phone numbers are not listed and only known to me and family, but they had addresses to homes, home phone numbers, mobile phones," Rhodes added.
The scandal that has shaken the British media like never before has already led to several heads rolling, including two top officers of the Scotland Yard, who quit over questions of their links to a former editor of the NOTW.
Rebekah Brooks, the former CEO of the News International had to step down over the scandal while Rupert Murdoch and his son James had to appear before a parliamentary committee to face tough questions.
Prime Minister Cameron too has come under fire for his hiring of a former editor of the NOTW and had to face jeers from the opposition benches when he defended himself in the House of Commons.