In an interview with Today presenter Justin Webb, Stephens, a lawyer with Finers Stephens Innocent, said he believes phone-hacking was taking place at many other news outlets.
His comments follow an announcement by lawyer Mark Lewis at the weekend that he has been instructed by four clients with complaints against other national newspapers.
In 2007, former News of the World royal correspondent Clive Goodman and private investigator Glenn Mulcaire were convicted of conspiracy to intercept telephone calls and earlier this month the tabloid announced it had suspended assistant editor (news) Ian Edmondson over a 'serious allegation' of phone-hacking".
Stephens said this morning that he thought the practice was used elsewhere "with just about every news organisation involved at some level or another", but that News International had been exposed as a result of the arrest of the private detective it used, Glenn Mulcaire.
"But the problem for News International has been that Glenn Mulcaire … was the person who wrote absolutely everything down, including the people who had commissioned him to do the work, so there was in that particular case, the legal smoking gun which enabled the proceedings to take place."
He added however that this is not the situation for other cases, which he said are therefore likely to "slip through to the keeper".
"The reality is that if you look at the chain of evidence, there isn't that continuum which allows legal action to actually get off the ground."
On Friday, former editor of the News of the World Andy Coulson resigned from his position as director of communications for Downing Street, citing the pressure of media coverage relating to allegations of phone-hacking at the tabloid.
Coulson has consistently denied having any knowledge of the practice while he was editor.
Following his resignation, Channel 4 News presenter Jon Snow alleged via Twitter that he suspected his voicemail had been hacked by a different newspaper. He has refused to comment further at this stage.