Caroline Kean of law firm Wiggin said that public figures such as Kate Middleton, who do not actively seek publicity, were suffering because of celebrities who do not exercise their right to privacy.
Middleton complained to the Press Complaints Commission (PCC)
through her lawyers Harbottle and Lewis after a picture of her walking to work was printed in the Daily Mirror last week.
The complaint was made under clause four (harassment) of the PCC editors' code of conduct. Middleton's lawyers have made several informal complaints since paparazzi pictures of her began to change hands for thousands of pounds last year.
Kean said: "You have a lot of people who are celebrities who want to have these stories published about them –— it's what I call the devil's pact. They go around pretending that they are not feeding stories to the press, but they are.
"A lot of these [celebrity stories], if brought in front of a court, would arguably be a breach of people's [privacy] but they are out there planting them and colluding with the press. This is where it gets very blurred."
"It's actually quite clear what the law is, but a lot of people who appear in the press don't want a private life."
Kean said Middleton was complaining to establish that she wants a private life.
She said: "The law says that everybody, whether they are a private person, or the girlfriend of the heir to the throne, has a right to a private life and that there are certain things such as their sex lives, home lives and relationships that are, on the face of it, going to be protected and treated as private.
"Someone like Kate Middleton photographed on the street — there is no public interest in publishing that picture.
At the moment, she is a private person."
Mirror editor Richard Wallace apologised for printing the picture, admitting the paper had "got it wrong".
In a page two story in Saturday's Mirror, Wallace said: "On Thursday, we published an innocuous picture of Ms Middleton walking down the street with a cup of coffee. It was taken by a freelance photographer in circumstances where we were later told she felt harassed. We got it wrong and we sincerely regret that."
A spokesman for the PCC said Middleton's complaint would be heard by its complaints committee, as planned, on 1 May despite the Mirror's apology.