LONDON - The press likes to cast itself as society's guardian. On Monday, the judge leading the investigation into Britain's deepening phone hacking scandal vowed to find an answer to the question: Who guards the guardians?

For years, the British media's answer has been that it mainly looks after itself. But following explosive revelations of pervasive criminality at Rupert Murdoch's News of the World tabloid, Lord Justice Brian Leveson suggested it was time for a change.

"Guarding the guardians is not an optional add-on," he said.

Britain's phone hacking inquiry was set up by Prime Minister David Cameron shortly after the scandal boiled over in July, pulling the lid off illegal spying at the nation's bestselling Sunday newspaper and exposing police corruption.

The tabloid's publisher, News International, had wrongly claimed the behaviour was confined to a single rogue journalist jailed over phone hacking in 2007. Since then, it's become clear that wrongdoing was rife at the paper, and perhaps other papers too. Leveson's inquiry is an attempt to restore ethical standards to a scandal-scarred industry.

Although the now-defunct News of the World has few defenders, editors and broadcast bosses have publicly voiced concern that a backlash could leave Britain's press less aggressive -- and less free.

While inquiry counsel Robert Jay said that the importance of a free press was "almost self-evident," he warned that the media may not necessarily like the solutions the inquiry finds for tricky ethical issues.

"These solutions will not necessarily have been the solutions which the press themselves would have devised," he said.

Leveson said he hoped to have the first part of his inquiry wrapped up by the end of 2012. He's expected to recommend either scrapping or radically reforming the Press Complaints Commission, the self-regulatory body whose failure to get to grips with the hacking scandal has been roundly criticized. The scope of his inquiry's recommendations will hinge in part on whether illegal behaviour is found to have been limited largely to the News of the World or whether it was practiced more widely.

There seemed to be plenty of evidence of the latter at Monday's hearing.

Jay told the inquiry -- whose proceedings were broadcast live over the Internet -- that it appeared that illegal interception of voicemails went beyond the News of the World. He said that the inquiry had seen the names of no fewer than 28 News International employees in the notes kept by Glenn Mulcaire, the private investigator which the News of the World paid to illegally eavesdrop on its victims.

The words "The Sun" -- a possible reference to the News of the World's sister-title -- also cropped up in Mulcaire's notes, Jay said. So too did a name linked to the Daily Mirror, the Sun's left-wing rival.

Jay said that the evidence on phone hacking pointed to what he described as, "at the very least, a thriving cottage industry."

The father of murdered schoolgirl Milly Dowler was among those attending the start of the inquiry.

Bob Dowler frowned as Jay told the hearing that the trigger for the inquiry was the revelation that his 13-year-old's voicemail had been hacked into by the News of the World at the height of the media frenzy over her disappearance in 2002.

Dowler's case was the first to arouse broad public anger when it was reported by the Guardian newspaper in July, though several celebrities had earlier won settlements from News International. Among the people who will be legally represented at the hearings are "Harry Potter" author J.K. Rowling, singer Charlotte Church, actor Hugh Grant and actress Sienna Miller.

Along with several dozen journalists backed into a room at London's neo-gothic Royal Courts of Justice were a handful of members of the public.

Katriona Ormiston, a 21-year-old journalism student, said she was there to see media history being made.

"Obviously it's got quite a big impact on the future," she said.