The British celebrity accused the Mail on Sunday newspaper, which is not owned by Rupert Murdoch's News International, of hacking into his phone for a story about his relationship with former girlfriend Jemima Khan.
The Daily Telegraph said Grant testified it was "inconceivable" the paper had obtained a story about his relationship with Jemima Khan any other way
He also implied police were leaking stories to the press, saying paparazzi showed up before police when his girlfriend was mugged.
Earlier, the parents of a slain British schoolgirl testified they had false hope their daughter was alive because a hacker had cleared the girl's voice mail.
The parents, Sally and Bob Dowler, accustomed to hearing a recording that their daughter's voice mailbox was full, said they were thrilled when they thought Milly Dowler had picked up her messages, The Daily Telegraph reported Monday.
But Milly Dowler's phone had been breached and messages were deleted by Glenn Mulcaire, a private detective hired by Murdoch's defunct News of the World.
"At first we were able to leave messages and then her voice mail became full ... so I was used to hearing that," Sally Dowler told a government inquiry. The inquiry was ordered by Prime Minister David Cameron after it emerged Milly Dowler, 13, who was abducted and killed, had been a subject of the phone-hacking scandal that forced the News of the World to close and resulted in the arrests of several members of the newspaper's management team.
"I rang her phone and it clicked through on to her voice mail and I just jumped and said: 'She's picked up her voice mails Bob. She's alive,'" Sally Dowler said. "When we heard about the hacking that was the first thing I thought."
She said the revelation about her daughter's phone being hacked had been "terribly difficult to process."
"We would sincerely hope that News International [parent of News of the World] and other media organizations would look very carefully how they procure, how they obtain information about stories. Obviously, the ramifications are far greater than what appears in the press," Sally Dowler said.
The mother told the inquiry into media culture, practices and ethics she didn't sleep for three days after learning her daughter's phone was hacked, the BBC said.
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