The much-awaited public inquiry into the News of the World phone hacking and the broader issue of ethics in British media began here on Monday with a warning to newspapers from Lord Justice Brian Henry Leveson, heading the probe, not to target witnesses who spoke out against them.

His warning came after revelations that some of the hacking victims and their lawyers had been tailed by a private detective hired by NoW.

Referring to concerns on the issue, Lord Leveson said: “And if it appears that those concerns are made out, without objective justification, it might be appropriate to draw the conclusion that these vital rights are being abused, which itself would provide evidence of culture, practice and ethics which could be relevant to my ultimate recommendations.”

He reminded journalists that right to free speech entailed the duty to make sure that it was exercised responsibly. At the heart of the inquiry, he pointed out in his opening statement, was “one simple question: - who guards the guardians?”

The press provided “an essential check on all aspects of public life” and any failure on the part of the media affected everyone.

“At the heart of this inquiry therefore may be one simple question — who guards the guardians?” he said.

Robert Jay QC, counsel for the inquiry, said it had not yet seen any examples of phone hacking that could “even start to be justified on public interest grounds”.

The inquiry will also look into the often cosy relationship between the media, the political establishment and the police revealed by the hacking scandal.

A number of high-profile politicians, media personalities, and police figures are expected to give evidence joining a long cast of victims of NoW hacking including the parents of Milly Dowler, the murdered teenaged schoolgirl whose phone was hacked by the tabloid's journalist when she went missing.

It was this revelation that sparked a chain of events leading to the closure of the 160-year-old NoW and a spate of high-level resignations at News International, Rupert Murdoch's British media group which published the tabloid.

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