France has one of the world's toughest privacy laws on paper, but the legislation is effectively toothless because the fines for breaching it are miniscule, legal experts and journalists say.

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Under Article 9 of the 1970 Civil Code, which Britain's Prince William and his wife Catherine will rely on if they decide to sue over topless pictures of the duchess, every person present on French soil has a right to privacy.

The principle was enshrined in a revised constitution in 1995 and covers the disclosure of details about a person's private life as well as the publication of images taken and published without their permission.

The law gives the state significant powers to block publication of intimate information or images but the consequences if media decide to "publish and be damned" are slim.

In theory, an editor breaching the law could face a one-year prison sentence and a fine of up to €45,000.

In practice, precedent suggests a purely symbolic fine is the most that offending publications risk, and even the maximum fine would be peanuts for a magazine like Closer, which on Friday published the pictures of the former Kate Middleton on holiday in the south of France.

The publication is the leader of a new pack of glossy magazines that have been breaking down long-established taboos surrounding the privacy of French politicians and celebrities.

Neil Wallis, a former editor of British tabloids, said Closer executives would not be the slightest bit worried about the prospect of legal reprisals.

"Frankly, for Closer magazine it will be a badge of honour," he told Sky News. "If they get taken to court, they will be delighted. They will make a relatively small payment. They're going to sell out with these pictures. It will be a straightforward calculation."

His view was echoed by advocate Isabelle Wekstein, an expert on French media law.

"The level of damages awarded, even with interest added, is generally quite low and publications budget for these kind of expenses."

Wekstein said a judge will consider the extent to which an individual is deemed to have exposed their private life to public scrutiny when deciding on the size of any fines.

"For example, if you are talking about a participant in a reality-TV show, then damages will be less high than if it was a public figure who reveals relatively little about his or her private life."

A court will also consider the quality of any pictures published, whether it goes on to front or inside pages, and whether there was any legitimate news interest associated with its publication.

"The obligation to publish a legal judgement on the front page is often the sanction feared the most by the publishers of people magazines because that deprives them of space in their 'shop window'." Wekstein said.