Hi QDM,
Short answer is no. For an altiport you need only a "site authorisation" from an instructor who is qualified to issue it.
Here's the long answer!
There are 2 classes of mountain landing site in France. "Altiports" and "altisurfaces".
Altiports are licensed airfields with published circuit patterns, which meet a number of criteria defined by the French DGAC (CAA). Altisurfaces are unlicensed airfields. Some of them have runways, some of them are rather basic. And some of them are glaciers.
There are 7 altiports in France (Megeve, Alpe d'Huez, Courchevel, Corlier, Meribel, another one in the Alps which I've forgotten, and Peyresourde in the Pyrenees). You can obtain a site authorisation for any of these, which allows you to use the altiport unaccompanied. The authorisation expires if you don't use if for 6 months.
To have unrestricted access to all the altiports, and to the altisurfaces, you need the full mountain rating.
This is a reasonable undertaking. It usually takes between 15 and 30 hours training, assuming you have a good general flying ability to start with. Good taildragger skills help, unless you use a Rallye - which is the only nosewheel type that is regularly seen at altisurfaces. Instruction has to be given by a qualified mountain instructor, of whom there are about 80 in France. At the end of the course there is an exam which covers general mountain flying skills (crossing passes, turns in valleys, assessment of wind and likely turbulence), landing at altiports, and landing at several different altisurfaces. Navigation is also covered, in that you are expected to find your way from one altisurface to the next without asking the examiner and without infringing any national or regional parks. (Navigation is a nightmare to start with when all the mountains look the same. After a while it becomes easier, and use of maps is very unusual.) The standard required for the test is high.
You can do the training in winter, on skis, in which case you qualify for the mountain pilot's rating with the "extension neige". To get this you will also have to train on glaciers and glacier landings will be added to your exam. The ski-qualification automatically entitles you to use altiports and altisurfaces when there is no snow - which is bizarre, and is being contested by the French mountain pilot's association. It is much easier to land with skis. If you train on wheels, you need to retake the exam on skis before you can land on a snow-covered altiport or altisurface.
Once you pass the exam, the instructor will sign your logbook to show you've passed. In France the mountain qualification is a formal rating which is added to the licence. For foreign licences this isn't possible; instead you will be issued an "attestation" showing your UK licence number and stating that you have met the conditions required for issue of a mountain rating and that you are therefore authorised to land and take off at altisurfaces. To get this document you need to provide your licence and logbook (or copies thereof) to the regional DGAC office. The logbook must show proof of adequate mountain training, and be signed by the examiner. You must also provide the exam report which is given to you by the examiner after the test. The DGAC makes no charge!
I hope this answers your question. If you are thinking of getting the rating, my advice is don't hesitate. The trianing is fun, the scenery is breathtaking, you will fly to some quite incredible places where it shouldn't be possible to land an aeroplane. You will train with instructors who are absolutely dedicated to their sport, and who are among the most skilled (and unassuming) pilots around.