Paul Silva says the younger sister of the former Kate Middleton typically has eight or nine photographers camped outside her door and estimated that they produce between "300 to 400 pictures" of her daily.
Silva was answering questions at the Leveson Inquiry, a judge-led investigation into the ethics of the country's media.
The inquiry was set up in the wake of the phone-hacking scandal centered on Rupert Murdoch's News of the World and has heard from celebrities who say they were hounded by paparazzi.
Silva said Wednesday that he saw no need to constantly run photographs of Pippa Middleton.
