Andy Coulson listened to intercepted voicemail messages left on the phones of public figures while he was editor of the News of the World, according to a former senior journalist on the Sunday newspaper.
The new witness in the long-running phone hacking scandal is the first to directly claim that Mr Coulson, who is now the Prime Minister's chief spin doctor, not only knew that reporters on the Rupert Murdoch-owned title were illegally obtaining voicemails but also personally checked recordings or asked for transcripts to ensure that stories were correct.
The unnamed former News International executive tells a Channel Four Dispatches programme due to be broadcast tonight that he would show Mr Coulson intercepted material while working alongside him. Mr Coulson has consistently denied that he knew about the phone hacking.
The newspaper's former royal correspondent, Clive Goodman, was jailed in January 2007 along with private investigator Glenn Mulcaire after both men admitted illegally accessing the voicemails of celebrities, including Princes William and Harry.
Mr Coulson resigned after the case, saying he accepted responsibility for the actions of his employees but had known nothing about them. He told a House of Commons select committee last year: "I am absolutely sure that Clive's case was a very unfortunate rogue case."
The Dispatches witness, whose words are spoken by an actor in the programme, said: "Andy was a very good editor. he was very conscientious and he wouldn't let stories pass unless he was sure they were correct... so, if the evidence that a reporter had was a recorded phone message, that would be what Andy would know about.
"So you'd have to say: 'Yes, there's a recorded message.' You go and either play it to him or show him a transcript of it, in order to satisfy him that... it wasn't made up."
The furore over alleged dialling into voicemails by private investigators and journalists, which threatens to provoke a slew of compensation claims from affected celebrities, reignited last month when another former NOTW reporter, Sean Hoare, told the New York Times that Mr Coulson had "actively encouraged" him to hack into phones.
The Channel 4 witness said: "It was fairly common – not so common that everybody was doing it. But the people who did know how to do it would do it regularly."
Scotland Yard has been criticised for its handling of the original investigation into the actions of Goodman and Mulcaire after it emerged that officers did not interview any other executives or journalists at the newspaper. The Dispatches witness added: "There were rumours every day of who they were coming for next. And then I think the feeling in the newsroom turned to surprise that nobody else was affected." The new allegations come at the start of a high-profile week for Mr Coulson as the Conservative Party looks to showcase its achievements at its annual conference in Birmingham.
It emerged at the weekend that the former NOTW editor could also be called to give evidence at the perjury trial of former Scottish Socialist Party leader Tommy Sheridan and his wife Gail, which is due to begin today. Mr Coulson has given a statement to lawyers acting for Mr Sheridan and was editing the London edition of the NOTW when it published the story over which the Scottish politician successfully sued for defamation in 2006.