The offices of French magazine Closer were raided this morning by police seeking information which would enable them to identify the photographer responsible for taking the topless pictures of Kate.

The raid followed the formal launch of an investigation by prosecutors in Paris on Monday, when William and Kate also won an injunction banning further distribution or publication of the images.

But the legality of the raid is under question.

Christophe Bigot, a barrister who specialises in media law, told French paper Le Figaro that photographers  are strictly protected by French law.

"A law of January 2, 2010 protects the confidentiality of sources, as do numerous decisions of the European Court of Human Rights," said Mr Bigot. "In the case of William and Kate, I do not see how a prosecutor could justify a search of Closer."

Referring to today’s raid, a police source said: "The aim is to seize any information which might lead to the identity of the photographer."

A local newspaper photographer has admitted being at the scene, and taking a picture of William and Kent by the chateau’s swimming pool, according to the Daily Telegraph.

But Philippe Minard, the managing editor of La Provence, insisted that Valerie Suau was not responsible for taking the topless pictures.