The prime minister's media adviser, Andy Coulson, personally listened to the intercepted voicemail messages of public figures when he edited the News of the World, a senior journalist who worked alongside him has said.

Coulson has always denied knowing about any illegal activity by the journalists who worked for him, but an unidentified former executive from the paper told Channel Four Dispatches that Coulson not only knew his reporters were using intercepted voicemail but was also personally involved.

"Sometimes, they would say: 'We've got a recording' and Andy would say: 'OK, bring it into my office and play it to me' or 'Bring me, email me a transcript of it'," the journalist said.

The claim, due to be broadcast tomorrow night, goes beyond earlier statements by Coulson's former colleagues.

Sean Hoare, a showbusiness reporter, told the New York Times Coulson had "actively encouraged" him to intercept voicemail.

Paul McMullan, who handled investigations, told the Guardian illegal activity was so widespread in the newsroom that Coulson must have known about it. Coulson has denied all the claims.

Channel Four's anonymous witness, whose words are spoken by an actor in the programme, says: "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 you weren't going to get sued, that it wasn't made up."

In evidence to a House of Commons select committee last year, Coulson said he could not remember any instance of voicemail being intercepted during his six years at the paper.

He resigned in January 2007 after the tabloid's royal correspondent, Clive Goodman, was jailed for listening to the voicemails of three members of the royal household. "I am absolutely sure that Clive's case was a very unfortunate rogue case," he told the committee.

Channel Four's witness said: "It was fairly common – not so common that everybody was doing it. That wasn't the case at all. But the people who did know how to do it would do it regularly."

Other journalists had expected to be drawn into the police investigation, the source said, adding: "There were huge rumours swirling every day of who they were coming for next and who was going to come and cart away this person, that person and the other. And then I think the feeling in the newsroom turned to surprise that nobody else was affected."

The programme includes claims that politicians and police have been cowed by fear of Rupert Murdoch's News International, which owns the News of the World.

Adam Price, one of the MPs from the media select committee which last year investigated the phone-hacking scandal, described how he stopped voting to compel News International's chief executive, Rebekah Brooks, to be called as a witness.

"I was told by a senior Conservative member of the committee, who I knew was in direct contact with executives at News International, that if we went for her, they would go for us – effectively that they would delve into our personal lives in order to punish them."

The Labour MP Tom Watson said he was threatened in 2006 after he called for Tony Blair to resign at a time when News International was supporting him.

"A very senior News International journalist told me that Rebekah would never forgive me for what I did and that she would pursue me through parliament for the rest of my time as an MP," he said.

Brian Paddick, a former deputy assistant commissioner at Scotland Yard who is also taking the police to court, suggested that his former colleagues' decision to cut short their original investigation may have been influenced by their links with the News of the World.

"That relationship was well worth protecting ... when you have something as big as this, where you're talking about potentially a large investigation involving illegal activity, you can see how potentially pressure could have been brought to bear," he said.

Dispatches raises an unresolved question over whether the officer who was in charge of the original investigation, the then assistant commissioner Andy Hayman, was himself a target of the News of the World.

When Channel Four asked him whether his name appeared anywhere in the evidence collected by his officers, he replied: "I have never been told whether my own telephone was hacked." Hayman now works for News International.

The programme is presented by the conservative columnist Peter Oborne, who writes for the Telegraph and is close to the Tory leadership.

Oborne says in the programme that voters supported David Cameron in order to restore a sense of decency in politics. He continues: "Instead, by hiring Andy Coulson, he has sanctioned the News of the World culture of impunity and got too close to the Rupert Murdoch power elite."