On fourth day of evidence to Lord Justice Leveson, stars say they were abused, spied on, followed and intimidated

JK Rowling told the Leveson inquiry into press standards that photographers had left her feeling under siege and like a hostage.

The Harry Potter author attacked newspapers for publishing pictures of her children, including one of her daughter in a swimsuit, revealing her family's home address, and placing a letter addressed to her in a schoolbag belonging to her five-year-old child.

The inquiry also heard from Sienna Miller, who said she had been spat at and verbally abused by paparazzi, as Lord Justice Leveson heard a fourth day of evidence from celebrities who claim they have suffered at the hands of newspapers.

Rowling, who gave evidence for nearly two hours, said: "There were two particularly bad periods when it really was like being under siege or like a hostage, after the birth of my … children. For a week it was impossible to leave the house without being photographed."

She said that some newspapers had honoured her repeated requests for her privacy to be respected. "But a significant section of the press have regarded that almost as a challenge."

Rowling explained she had sold the home she bought with the proceeds of the first Harry Potter book because it faced on to a road and the attention from photographers had become intolerable. After moving, her family were periodically placed under what she described as surveillance.

One one occasion, she called her public relations agency to ask why photographers from a Scottish tabloid were outside her house and was told: "It's a boring day at the office." "There wasn't even a sense there was a story. So my family and I were literally under surveillance for their amusement," she said.

"It's a very unnerving feeling to know that you're being watched."

Rowling said she felt "a sense of invasion" when she found a note in her daughter's bag when she returned home from primary school. "It's very difficult to say how angry I felt that my five-year-old's school was no longer a place of complete security from journalists."

A photograph of her young daughter, who was then eight, in her swimming costume that appeared in OK! magazine in 2001 could still be found online months after it was taken down by the paper which published it, she added, and would probably never be completely removed.

"Unlike an untruth that is in print … when an image is disseminated it can spread around the world like a virus."

Rowling said that she had been the subject of unwanted attention from "unbalanced people" and objected to the fact several newspapers had published pictures of her properties that were clearly identifiable.

"It's not because I'm being showy or precious," she said. "It's because on a number of occasions the police have been involved because of incidents or even threats."

She said the Evening Standard was among the papers who had done this. "The attitude sees to be utterly cavalier," she said. "Indifference. 'What does it matter? You're famous. You're asking for it.' "

Rowling also told the inquiry she felt like she was being blackmailed in 2003 when the Sun allegedly offered to return a stolen copy of a yet-to-be-published fifth Harry Potter book to her in exchange for a photo opportunity.

Rowling also revealed she had been told by the information commissioner that she had been targeted by private investigator Steve Whittamore. "He seemed to be making extensive inquiries about my extended family," she said.

Sienna Miller had earlier described how she was followed by around 15 men on a daily basis when she first became famous at the age of 21. "It's very intimidating," the actor said, adding: "Because they have cameras, it's legal."

The actor criticised the Daily Mirror for publishing a picture of her pretending to be shot by a young child at a charity event, but removing the image of the boy and claiming she had been drunk.

"I sued, I won, they printed an apology that was minuscule … but by that point the damage is done."

Rowling and Miller both said they felt the Press Complaints Commission, the industry body funded by newspapers, was ineffectual.

In her witness statement to the inquiry, Rowling wrote: "In my view, given my personal experiences, the PCC cannot be trusted to do its job and regulate the press within the rules of law, as the press seems to be free to act as they wish, and they publish my private and highly sensitive information without any sanction.

"I feel the PCC is toothless. It is a wrist-slapping exercise at best. I do feel that we need a body that has teeth – that can impose sanctions."

Miller told the hearing that even the threat of legal action did not prevent newspapers from publishing incorrect or defamatory stories. "The fact that they knew that they would be fined and have to pay damages was really not enough of a deterrent," she said.

The actor successfully sued the News of the World's owner, News International, after it hacked her mobile phone, and won damages of £100,000 earlier this year. She felt paranoid and anxious when articles about her private life appeared in the paper, and had falsely accused close friends and relatives of leaking information about her, she said.

The former Formula One boss Max Mosley told the inquiry that the News of the World had set out to destroy him after he sued the paper for running a front-page story about his sex life.

He told the inquiry that after he challenged the tabloid in court, it responded by sending a film of him participating in an alleged sadomasochistic orgy to the governing body of world motorsport.

Mosley also criticised Paul Dacre, the editor of the Daily Mail, who has accused Mosley of indulging in "unimaginable depravity".

"I have no idea what Mr Dacre's sex life is, all I know is that he has this sort of preoccupation with schoolboy smut in his website, Ms X in her bikini, Ms Y showing off her suntan," Mosley said, referring to the paper's website.

"So maybe he has some sort of strange sex life but the point is it's not up to me to go into his bedroom, film him and then write about it."