A former News of the World editor said today that he feared there were "bombs under the newsroom floor" in the form of a history of illegal practices at the paper.
Colin Myler told the Leveson Inquiry into press standards he felt "discomfort" over the extent of phone hacking among the now-defunct Sunday tabloid's journalists.
He became News of the World editor in January 2007 after Andy Coulson resigned following the jailing of the paper's royal editor Clive Goodman and private detective Glenn Mulcaire.
Mr Myler told the inquiry: "It's fair to say that I always had some discomfort and at the time I phrased it as that I felt that there could have been bombs under the newsroom floor.
"And I didn't know where they were and I didn't know when they were going to go off.
"That was my own view. But trying to get the evidence or establishing the evidence that sadly the police already had was another matter."
Mr Myler stressed that he did not believe phone hacking went on at the News of the World while he was editor.
He said he assumed that the police inquiry into the illegal interception of voicemail messages by the paper, which resulted in the convictions of Goodman and Mulcaire, had not uncovered evidence against other journalists.
Noting that detectives took away three black bin liners of material when they raided Mulcaire's home in August 2006, he said he initially accepted the line that hacking was restricted to one "rogue reporter".
The former editor said: "Given what I believed to be a thorough police investigation throughout that period, and the fact that the police had not interviewed any other member of staff from the News of the World other than Mr Goodman, I think that weighed heavily on my mind.
"I assumed that they would have done so if they had any kind of evidence or reason to speak to somebody else."
But Mr Myler said he changed his view after seeing the "For Neville" email, which contained transcripts of illegally intercepted voicemail messages and was apparently destined for the News of the World's chief reporter Neville Thurlbeck.
He told the inquiry: "It (the rogue reporter defence) couldn't be correct in as much as the 'For Neville' email indicated that at least another reporter had transcribed it and it named another reporter."
Mr Myler denied that the News of the World carried out a "cover-up" by paying Professional Footballers' Association chief executive Gordon Taylor £425,000 plus costs to settle his claim over the hacking of his phone by the paper.
But he accepted that the company wanted to avoid the embarrassing publicity that could have resulted if the case had gone to trial.
Robert Jay QC, counsel to the inquiry, suggested: "You mentioned the bombs under the newsroom floor, but this was creating a tendency for one or more of those bombs to explode if there were a trial."
Mr Myler replied: "Possibly that would have been the case... The company, not unreasonably or unsurprisingly, wanted to try to get things back on track after Mr Mulcaire and Mr Goodman went to jail.
"And it was a significant process to do that. So there was no appetite to go back to that place."
He said he did not subscribe to the stance taken on fact-checking stories by former Sun editor Kelvin MacKenzie, who told a Leveson Inquiry seminar in October: "My view was that if it sounded right it was probably right and therefore we should lob it in."
Mr Myler told the inquiry: "I have never been of the 'lob it in' school of journalism.
"I may have been accused of being negligent, but I haven't gone into a situation intending to be negligent."
He added: "Most journalists that I know today, and certainly editors that I know, have incredibly high standards of ethics, of professional ability and total understanding and respect for the law and certainly the PCC (Press Complaints Commission)...
"The manner in which we are perhaps all being tainted as being reckless and negligent, 'it's a Wild West out there' and 'if it sounds right, lo' it i" - it's just not there, in my experience."
Mr Myler was critical of harassment by paparazzi and called for the industry to "reflect on certain matters of decency".
He said: "The saddest thing is that the collective brain power amongst those who produce newspapers, it's pretty magnificent, and if only they could drop some of that commercial rivalry, understand and face the problems and issues that affect all of them.
"This is not about broadsheet, broadcast media against the red tops...
"Unless the industry really does come together and unite and engage with courts, with the judiciary, with politicians and agree that things do have to change from both sides and all sides, not just on ours, I think it's a pretty gloomy and grim future.
"But I hope that doesn't happen and I hope that through this inquiry they will be able to unite and come together on common ground."
Meanwhile, former News of the World reporter Daniel Sanderson said he understood the paper would not publish the personal diary of missing Madeleine McCann's mother without her express permission.
Kate McCann told the inquiry last month that she felt "violated" when the intensely private journal appeared in print in September 2008.
Mr Sanderson arranged to buy a Portuguese translation of the diary from a journalist in Portugal, had it translated back into English, and wrote up a story about it, the inquiry heard.
But he said it was left to Ian Edmondson, the News of the World's head of news, to clear its publication with Mrs McCann.
"I was told at the time that we would not be publishing the diary unless we had specific, express permission from the McCanns," he said.
Mr Sanderson said he would apologise to Mrs McCann after giving evidence to the inquiry, adding: "I did feel very bad that my involvement in the story had made Mrs McCann feel the way that it had."
Private investigator Derek Webb told the inquiry that he placed about 150 people under surveillance while working for the News of the World between 2003 and July this year, when the paper closed.
Mr Webb, a former Hertfordshire Police detective, said 85% of them were celebrities or MPs and the remaining 15% were lawyers or people connected to crime or drug-taking.
He said the targets he was commissioned to follow included Labour MP Tom Watson and former celebrity couple Sienna Miller and Jude Law.
The investigator told the hearing he was also tasked with carrying out surveillance on two lawyers - Charlotte Harris and an unnamed man - to see if they were having an affair.
He said he followed and filmed a woman during this assignment, but was told by the News of the World that it was the wrong person.
Mr Webb said the paper's chief reporter, Neville Thurlbeck, contacted him in early 2009 and told him to join the National Union of Journalists, terminate his private investigator's licence and change his firm's name from Shadow Watch to Derek Webb Media.
"He told me it's in relation to the Clive Goodman affair, that because of the use of previous investigators - ie Glenn Mulcaire - that they didn't want to be tied up with private investigators," he said.
Prime Minister David Cameron set up the Leveson Inquiry in July in response to allegations that the News of the World commissioned Mulcaire to hack murdered schoolgirl Milly Dowler's phone after she disappeared in 2002.
The first part of the inquiry, sitting at the Royal Courts of Justice in London, is looking at the culture, practices and ethics of the press in general and is due to produce a report by next September.
The second part, examining the extent of unlawful activities by journalists, will not begin until detectives have completed their investigation into alleged phone hacking and corrupt payments to police, and any prosecutions have been concluded.
The inquiry was adjourned until Monday.