Allan I can report that the local gendarmerie have carried out an an exercise some months ago where they were pulling all foreign plated cars (out of the holiday periods) - aminly Dutch and belgian round here - and checking documentation, registration, insurance etc. From the questions it does seem as if they were looking for vehicles that should have had French registration, but were still on foreign plates. Since our car was legit, I cannot say what would have been the consequence if there was a mismatch - foreign plate, French insurance, so while there does not appear to be any great push in this area, it would be a mistake to assume it never happens.