I am a Brit based in France, where I've done all of my helicopter flying (including the training). Just to say most of the above is correct - although just to be precise, the permit or 'carte' is named and for a physical person (not a company) and you do not need to prove that you have no criminal record (I guess they look for themselves). As far as I am aware, there is no minimum time required to qualify for this permit (I had less than 100hrs). It is obtained from the
Préfecture de Police in Paris, and is valid for all French territory.
Again, to be precise, you then fax warning of each landing at an off aerodrome location (before the landing, even 1 hour before) and must have written permission of land owner.
Apparently, this exists to help protect against criminal activity using helicopters (smuggling, prison escapes, etc.).