Grant told the Leveson Inquiry in November that a “bizarre” article suggesting he had “late-night phone calls with a plummy-voiced studio executive” could only have come from listening to his voicemails.
“I cannot for the life of me think of any conceivable source for this story in the Mail on Sunday except those voice messages on my mobile telephone,” he said.
But Liz Hartley, head of editorial legal services at Associated Newspapers, which publishes the Daily Mail, the Mail on Sunday and Metro, rejected the claim.
She told the Leveson Inquiry the story came from a “trusted” source who spoke regularly to Grant’s then-girlfriend Jemima Khan.
“I think that to make a very serious allegation against us, on something as thin as this, was not something that should have been done,” she said.
Hartley said her view was that Associated Newspapers would “stand by” a statement issued by the Mail on Sunday accusing Grant of “mendacious smears” in his evidence to the inquiry.
“If you’re going to make what are going to be widely publicised allegations, you ought to be careful about what you say,” she said.
“And if you choose to make allegations, which he’s perfectly entitled to do, it should come as no surprise when those are very robustly defended.”
Hartley said the statement accusing Grant of “mendacious smears” was drawn up by a number of people, including Associated Newspapers editor-in-chief Paul Dacre.
She said that she warned the actor after he publicly accused Associated Newspapers of being involved in phone-hacking several months before he gave evidence to the inquiry.
“In an endeavour to be of assistance and helpful and to avoid mistakes being made with serious consequences, I spoke to his representative and explained our position to him and followed it up with an email,” she said.
David Sherborne, counsel for Grant and other alleged victims of press intrusion, asked for the reporters who wrote the story about the “plummy-voiced” woman to be called before the inquiry when Dacre gives evidence on February 6.
He said: “Ms Hartley was prepared to offer her personal view about the ‘mendacious smear’ allegation but cannot explain how the newspaper came to actually accuse Mr Grant on the basis of no evidence at all.
“It’s clearly for Mr Dacre now to deal with how this ‘mendacious smear’ allegation was made.”