A former reporter at Britain's News of the World made a rare, robust defence of phone hacking on Tuesday, telling Britain's media ethics inquiry that eavesdropping on voicemails was a "perfectly acceptable tool" to help journalists uncover stories.

Paul McMullan said hacking was common at the now-defunct tabloid, describing how reporters traded the phone numbers of celebrities and accessed their messages by entering factory-set passcodes.

"I think I swapped Sylvester Stallone's mother for David Beckham," he said, going on to recount how he failed to hack into Beckham's voicemails on one occasion because the soccer star unexpectedly answered the phone.

McMullan, who now runs a pub in the English port of Dover, made headlines earlier this year when he was secretly taped by actor Hugh Grant claiming phone hacking was widespread at the News of the World and other UK newspapers.

He repeated that assertion today, adding that the bosses at the News of the World, including former top editors Andy Coulson and Rebekah Brooks, knew of the practice, a claim both former editors have denied.

Both resigned in the scandal - Brooks from a senior role in Rupert Murdoch's media empire, and Coulson from his job as top communications aide to Prime Minister David Cameron.

"I don't think anyone realised that anyone was committing a crime at the start," McMullan said. "Phone hacking is a perfectly acceptable tool given the sacrifices we make, if all we are trying to do is get to the truth."

Cameron set up the media inquiry in response to the scandal that began with the exposure of illegal eavesdropping by the News of the World.

Murdoch shut the tabloid in July after evidence emerged that it had accessed the mobile phone voice mails of celebrities, politicians and even crime victims in its search for exclusives.