The law mentions that it is forbidden to do so "sous réserve" (not sure how to translate that, "without prejudice" ?) of international treaties. I'd be surprise

The law mentions that it is forbidden to do so "sous réserve" (not sure how to translate that, "without prejudice" ?) of international treaties. I'd be surprised if there were no such treaty between France and the UK, or if it wasn't part of the EU treaty.