Just as a final pass on this subject, and perhaps for the info of other forumites, I have received this note back form Dunkerque
"usage restreint" means that you need ask clearance before coming (by letter or phone) (it's because we have no TOWER)
And as we invite you to come, you'll be welcome with pleasure.
For further information, we never refuse when pilots ask for clearance to come and visit us.
We remain at your disposal for further information
So it would appear that anyone can fly in there so long as you have asked.
Regards