Ex-News of the World editor Andy Coulson, who is accused of conspiring to hack phones, knew "exactly what went on on his watch", a former reporter has told the Old Bailey.
Dan Evans, who has admitted phone hacking, said his activities were "completely understood" by superiors.
He said "even the office cat knew" about phone hacking at the paper.
Mr Coulson denies conspiracy to hack phones and conspiracy to commit misconduct in a public office.
In clashes with Timothy Langdale QC, for Mr Coulson, Evans said one of his superiors had extensive knowledge of his phone hacking but maintained a pretence in editorial conferences that nothing was going on.
There were no other efforts to conceal the activity, Evans added.
"It was lip service only," he said. "It was an illegal activity.
"I did not necessarily want it to be an open secret but that is the way it became, a newspaper is a leaky place."
He told the court that at one point, there were three or four phones on his desk at the newspaper's office that were used for hacking.
Asked about who at the now-defunct newspaper knew about the phone hacking, Evans said: "The truth is that Andy Coulson knows exactly what went on on his watch."
He told the court how the depth of his involvement in phone hacking drove him to drink and drugs.
"There [was] a lot of duress," he said. "I had to get the stories to keep my head above water - it is difficult to understand the pressure people come under in newspaper land."
Evans earlier told the court he was "toeing the line" when he initially lied to police after he was caught trying to hack into designer Kelly Hoppen's phone.
The jury heard he "bitterly regretted not taking a braver course of action".
Evans was arrested in August 2011 and produced a prepared statement for police which he told the Old Bailey was "cobblers".
He said he had been "maintaining the lie", claiming "the sticky keys defence" - that Ms Hoppen's phone may have been hacked accidentally because Evans's mobile phone had damaged keys.
Evans later changed his story, admitted phone hacking and became a witness for the prosecution.
The reporter was challenged over his claim during evidence on Tuesday that Mr Coulson exclaimed "Brilliant!" when he heard a tape of Sienna Miller's voicemail message to Bond star Daniel Craig.
The court heard that the actress left a message for Mr Craig saying she loved him and that she was out with her then-boyfriend, Jude Law.
"It is truthful evidence," Evans said "The general context of the exact word, brilliant, I was paraphrasing. I think the word came out of my mouth as... trying to explain the general sense of how happy he was."
Evans told the Old Bailey that when he previously worked for the Sunday Mirror, he threw 10 pay-as-you-go mobile phone handsets he used for hacking in the River Thames.
He said he also "smashed up and binned" two untraceable phones he used after joining the News of the World because the paper's office was too far away from the river.
The jury has heard that Evans pleaded guilty to hacking at the Sunday Mirror between 2003 and 2005 and at the News of the World up to 2010. He also pleaded guilty to misconduct in a public office between 2005 and 2010.
Evans also confirmed he had admitted intending to pervert the course of justice.
The court was told he entered into an agreement with the Crown Prosecution Service in 2012 and has given two statements since.
Mr Coulson, 46, is one of seven people who deny charges related to phone hacking.
He also denies conspiracy to commit misconduct in a public office.