Interesting!
I am in the same boat as you FFF in that I hold an FAA IR which at some point I am intending to get converted into a JAA.
If you have done a recognised JAA conversion course, sat the exams and the flight test and got the piece of paper - can they deny the right to apply? If so on what grounds? Would be interesting to see the first person to challenge this in the courts if the French (or anyone else), did decide not to recognise it.