Harry Potter author JK Rowling has spoken at the Leveson inquiry of her horror at discovering a letter from a journalist inside her five-year-old daughter's schoolbag.

In a two-hour appearance before Lord Justice Leveson at the high court on Thursday, Rowling told of how she frequently felt "under siege" from photographers and gave a string of examples of alleged press intrusion.

Rowling said the most "outrageous" intrusions were when journalists targeted her children at school. "In the first burst of publicity surrounding [Harry Potter] … I unzipped her schoolbag in the evening; among the debris I found an envelope addressed to me from a journalist," Rowling added.

"It's my recollection that the letter said that he intended to ask a mother at the school to put this in my daughter's bag … I don't know how this got in my daughter's schoolbag.

"I can only say that I felt such a sense of invasion that my daughter's bag … it's very difficult to say how angry I felt that my five-year-old daughter's school was no longer a place of complete security from journalists."

Later Rowling recalled how a journalist from the Scottish Sun had contacted the headmaster of her daughter's school, claiming that there had been complaints about her daughter from other pupils and parents.

"My daughter was being accused of some kind of bullying," she said. "There was not one word of truth in it … To approach my daughter's school was outrageous."

Rowling told the inquiry how she had routinely felt "under seige" and "held hostage" by paparazzi photographers outside her house.

The author said that she had once hid her children with blankets inside their own home to protect them from the photographers outside.

"There's a twist in the stomach as you wonder what do they want, what have they got? It feels incredibly threatening to have people watching you," she said.

Following the birth of her son, Rowling said she was unable to leave the house for a week without being photographed and added that she once gave chase to a member of the paparazzi while with her children.

"The cumulative effect becomes quite draining," she said. "On a general note, the sense of being often unable to leave your house or move freely is obviously prejudicial to a normal family life."

Rowling also told how she was unsucessfully targeted by a journalist who claimed to be a Post Office employee in order to "blag" personal details about her. A journalist purporting to be a tax worker later sucessfully blagged personal details from her husband, she claimed.

"If you lock horns with certain sections of the British press you can expect retribution pretty quickly," she said, claiming that the attitude on tabloid newspapers was "utterly cavalier, indifference, what does it matter? You're famous; you're asking for it."

Earlier at the inquiry, the former Formula One boss Max Mosley told the inquiry how it felt like News International had been out to "destroy" him after he took the News of the World to court for breach of privacy.

• To contact the MediaGuardian news desk email editor@mediaguardian.co.uk or phone 020 3353 3857. For all other inquiries please call the main Guardian switchboard on 020 3353 2000. If you are writing a comment for publication, please mark clearly "for publication".

• To get the latest media news to your desktop or mobile, follow MediaGuardian on Twitter and Facebook